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All About Pearls (Glossary L – Z)

All About Pearls (Glossary L – Z)

wholesale pearlsLustre
The radiance of a pearl. The greater the lustre the greater the value. The highest lustre gives almost mirror-like or metallic reflections.

Mabe
A blister pearl which has been hollowed out and filled with a substance and backing. Mabe pearls are often made into earrings A mabe is a hemispherically shaped pearl which is grown against the inside of the oyster’s shell, rather than within its tissue Blister pearls are worked by cutting the pearl out of the shell with a circle-bit drill. The nucleus is then removed and replaced with a resin. The back of the pearl is capped with a piece of mother-of-pearl to complete the mabe pearl.

Maeshori
This is a Japanese term which means before (mae) treatment (shori). It encompasses treatments used on all akoya, freshwater and some South Sea pearls. Maeshori treatments vary from factory to factory. The processes tighten the nacre and pull moisture out to enhance the lustre. This has a side effect of tending to make the nacre more brittle, so that freshwater, pearls that have been over treated will turn chalky very quickly Maeshori processing on South Sea pearls is very common in Japan. It makes the pearls whiter, brighter, and more saleable.

One basic maeshori process is tumbling in chips of walnut shell which cleans and burnishes. Majorica or Majorcan pearl A high-quality fake pearl manufactured in Spain by Majorica, S.A. These nuclei are dipped in high quality essence d’orient ( varnish made up of the scales from bleak, shad, herring and salmon. 2,000 fish make one litre of essence, which is an organic substance similar to uric acid.)

Mantle tissue
The special tissue inside certain molluscs which secretes nacre

Metallic Lustre
A pearl has a metallic lustre when the lustre is so shiny that it resembles polished metal. Metallic lustre is not a criterion in the usual grading system

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Momme
A momme is unit of weight, used for silk or pearls, and you will still sometimes see pearl prices quoted as per momme – with the price given against quality. One momme is 3.75 grams and one Kan is 1000 momme

Nacre
is composed of layers of calcium carbonate (in a crystalline form) and conchiolin (an organic protein substance which provides bonding). The specific lustre, iridescence, and colouring of nacre — and, therefore, of any pearl which it forms — depends on the number and thickness of the various layers, as well as on whether or not the layers overlap one another. A freshwater pearl is made up of many layers of nacre and no bead. You can see the structure in this
pearl which split open:

Natural
A pearl which is ‘wild’ ie one which has grown without any human activity or intervention is called a natural pearl. Natural pearls are very rare these days and so command high prices. Scotland holds much of the world’s remaining population of freshwater mussels Margaritifera margaritifera, and they are protected by law under the Wildlife and Countryside Act 1981. Selling a Scottish natural pearl needs a licence. These molluscs can live for over 100 years. The earliest reference in Britain to freshwater mussels is by Julius Caesar’s biographer, Suetonius, who stated that Caeser’s admiration of pearls was a reason for the first Roman invasion in 55BC.

Orient
Orient comes from the thin-film interference and light diffraction caused when light passes through the nacre of a pearl. The iridescence, or lack thereof, is caused by the size of the aragonite platelets on the surface of the pearl

Parure
A matched set of jewellery, which might include earrings, a necklace, brooches, rings, and other pieces.

Peanut
A peanut pearl is formed when two nuclei in a seeded pearl stick and then grow together to make something which resembles the shell of a peanut.

Pearlescence
Resembling pearl or mother-of-pearl in iridescence and lustre (or, of course, an excellent source of all things pearl)

Pick a Pearl
A marketing ploy used in some tourist shops whereby the customer selects a shell which has been pre-seeded with a pearl of some sort, and lo – there is their pearl. Look closely and the mollusc is preserved in chemicals and long dead and the pearls usually freshwater. Pearlescence heard of one operation in the UK where someone got a dyed green potato pearl and was told it was green because the oyster was sick. Miss Joaquim Pearls knows where to buy these seeded molluscs for under $1 a time in China. But wouldn’t.

Pinctada maculata
This is possibly the smallest of the oceanic pearl producing oysters and possibly the direct ancestor of all of them. It produces bright, lustrous deep golden pearls but is too small to be farmed on a realistic commercial basis

Pinctada margaritifera
This mollusc produces the black Tahitian pearl in French Polynesia, the Cook Islands and Australia

Pinking
A very common to routine treatment especially for akoya pearls whereby the pearl, after bleaching, is dyed so that it shows a tinge of pink.

Pondslime
Pondslime is the name given to pearls which show an unusual golden to brown coating to their natural colour nacre. These pearls used to be either discarded as junk or dyed dark colours to disguise what was seen as a failure in cultivation but now such natural effects are valued and desirable. The effect ranges from a dull nicotine brown to dazzling gold as if the pearl has a layer of gold leaf

Popcorn
Pearls are pearls of any shape on which the surface nacre has a granulated appearance so that they look like fresh popcorn. We call them granulated pearls. Also called rosebud or strawberry pearls and in China, mao-jyue or hairy pearls.

Potato
Any mis-shapen pearl is a potato pearl because it resembles a potato. Also called irregular pearls or nugget pearls.

Pteria sterna
The rainbow lipped oyster which produces the pearls of the Sea of Cortez, Mexico These pearls fluoresce red under ultra-violet light.

Rice
Oval shaped pearls

Rice Crispie Pearls
Chinese freshwater pearls were originally grown in the Cristaria plicata (cockscomb pearl mussel) and resembled rice crispies.

Rosebud
see popcorn

Round
The more perfectly round a pearl is, the more valuable. A good quick way to assess roundness is to gently roll a strand of pearls. Irregularities will show easily to the eye

Scottish River Pearls
Highly prized and very rare wild natural pearls. So protected by law that a licence is needed to sell them. The species is Margaritifera margaritifera . They are believed to live for 250 years! It is said that one reason for the Roman invasion of Britain was to gain access to the pearls.

Sea of Cortez
One farm is producing mostly greys and blue shades in Mexico, re-starting a pearl history which was thriving when the Spanish invaded

Second Graft
What it says – a second graft happens when a mollusc is returned to the water after harvest. Its pearl sac is either re-filled, with a bead equal to the size of the pearl removed (so that the second pearl grown will be larger when that is harvested) or a keisi pearl will grow.

Seed pearls
Tiny naturals weighing under 1/4 grain, usually 33mm or less.

Shape
The rounder the pearl the more valuable it is.

Silver nitrate
This chemical, the same as used in photography, darkens the appearance of pearls. The chemical penetrates the layers of nacre and has a chemical reaction with light and hydrogen sulphide gas to create a rich black colour.

Size
Generally, the bigger the pearl the more valuable, however a smaller more perfectly formed round pearl will be more valuable than a big baroque one

Souffle Pearls
Very large freshwater pearls are being produced with pearls nucleated with a lump of mud (!) these pearls, third graft, can have stunning lustre and a rather keishi appearance so far. When drilled the mud is drained away so that the pearl is hollow and light in weight. However most freshwater cultured pearls are still solid pearl nacre, even pearls up to 15mm. This means that they are arguably more durable but the chances of non-perfect round shapes are higher.

South Sea pearls
Large South Sea cultured pearls (up to 16 mm), farmed in Australia, Indonesia, and the Philippines, range in colour from white to gold and to black. They can have a perfectly round to slightly asymmetrical shape and medium to high lustre Price varies depending on lustre. South Sea pearls are harvested after at least 2 years. They have a unique, satiny lustre that comes from the rapidly deposited nacre and warm waters of the South Seas. South Sea pearls also have a subtle array of colours, typically white, silver, and golden, Gold south sea pearls come mainly from Thailand and white south sea pearls mainly from Australia,

Spat
baby oysters which are either artificially bred in a hatchery or spawn naturally and are attracted to collection points are called spat. They will be grown on until big enough to be implanted

Sterling Silver
Sterling silver is a mix of 92.5% by mass of silver and 7.5% by mass of other metals, usually copper. The copper is added to make the metal harder. All Pearlescence Sterling silver over the required minimum weight carries the London Assay office hallmark of owner Wendy Graham (Initials wmg in an oval cartouche). All silver from Pearlescence is nickel-free.

Stick
Any long thin and stick or twig like pearl, They can be drilled at the top or middle and through the wider or narrower faces to produce different looks.

Surface.
The smoother and more perfect the surface of a pearl, the higher the value

Tahitian
Pearls are produced by the black-lipped oyster (Pinctada margaritifera). They have been produced for almost exactly 50 years now in French Polynesia, in the lagoons of remote coral atolls and islands – everywhere except on Tahiti Itself! Black Lip Oysters are now also being farmed in a small way in Australia.

The oyster itself is quite large — sometimes up to 12 inches across and weighing as much as 10 pounds — which often results in much larger-than-average pearls. The pearls are unique because of their natural dark colours. Most “black” Tahitian pearls are not actually black, but are instead grey, silver, charcoal, or similar shades. Truly black pearls are extremely rare. For reasons which are not known the black-lipped oyster produces circle pearls, which are usually
drop shaped and look as though the pearl has spun around in the pearl sac, so that there are banding patterns around the pearl in both colour and surface. Some prefer circle pearls because they are clearly real and not imitation. Tahitian pearls go through x-ray inspection before legal export (ask to see their export certificate and confuse most jewellers!) and have a different grading system A-D where A grade are the best pearls

Third graft
Sometimes molluscs yield pearls of such quality that farmers put them back in the water for a third time. Third graft pearls will be very large indeed, and the mollusc could be ten years old.

Top drilled
Asymmetrically drilled pearls, often oval. If strung un-knotted they tend to move around against each other on the silk and then are called dancing pearls

Vermeil
Vermeil is a plating of gold onto sterling silver. It is hallmarkable and a response to the high present cost of gold. All Pearlescence vermeil is nickel-free. Vermeil will be marked as sterling silver with metal. the gold must be at least 10ct (42%) and be at least 2.5micrometres thick. Nb American Vermeil often has a layer of nickel.

Wearing pearls
Do not put any hairspray, make-up, perfume or any other such substances where they could contact and be absorbed by the pearls. Pearls are a natural biological substance and are porous, so avoid anything which could be absorbed by them. We have reeled back in horror when opening envelopes for some pearls returned for re-stringing where they seem soaked in perfume.

Wish Pearls
see pick a pearl

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We send your purchasing parcel via FedEx, we inform you the tracking number as soon as possible
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All About Pearls (Glossary D – K)

All About Pearls ( Glossary D – K )

wholesale pearlsDye
Freshwater pearls especially are often dyed. Any very bright colour or deep colour is certainly dyed – there are no natural green, blue, red, purple etc freshwater pearls, at least so far. There is a wide choice of organic and inorganic dyes available and they are all permanent. Gold south sea pearls can also be dyed to deepen their colour (and value)

Edison Pearls
This is the brand name given to a range of large bead nucleated freshwater pearls from one leading Chinese supplier. One strand of these pearls achieved £1/2m at auction. The pearls come from a Hyriopsis hybrid between Hyriopsis cumingi and Hyriopsis schlegeli.

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Farm
Nearly every pearl available anywhere in the world is farmed – cultured. Pearl farms tend to be stunningly beautiful places.

Faux Pearl
Fake. A false pearl bead manufactured by coating the inside of a hollow glass sphere or the outside of a solid glass or plastic sphere with a pearlescent coating which is sometimes pearl powder. Faux is a fancy word for fake. Also called shell pearls. They are of course perfectly round in shape, with great lustre and even colour. White shell pearls are very white, which is a give-away. All fake pearls feel smooth when rubbed on the teeth and the drill holes tend to be larger.

Fiji
There is a young but growing pearl industry in Fiji, and the pearls produced have a huge and stunning range of colours.

Freshwater
A pearl grown in a freshwater river, lake or pond margaritifera mollusc. Often more irregular in shape and more varied in colour than salt water pearls freshwater molluscs are nucleated by creating a small incision in the fleshy mantle tissue and inserting a piece of mantle tissue from another oyster. This process may be completed 25 times on either side of the mantle, producing up to 50 pearls at a time. The molluscs are then returned to their freshwater environment where they are tended for 2-6 years. The resulting pearls are of solid nacre, but without a bead nucleus to guide the growth process, the pearls are rarely round.

Gamma Radiation
Gamma irradiation turns the nacre of freshwater pearls very dark, and often also imbues a metallic lustre with rainbow orient. Strangely, it has no effect on salt water nacre but will turn the nucleus dark which shows through the layer of nacre, making the pearl look grey or blueish There is no danger of radiation contamination from irradiated pearls.

Granulated
or popcorn pearls have a knobbly surface which resembles..popcorn. This granulation is often mixed with patches of high lustre surface. When the Chinese freshwater pearl business was starting up most of the pearls were, at least to some degree, popcornish and oval in shape. They were called Rice Krispie pearls.

Gold Leaf Pearls
This is the name we give to the extremely beautiful lustrous gold pearls which are natural pearls with a layer of aragonite with an incredible lustre – so it does indeed look as if a layer of gold leaf has been applied to the pearls.

Gold-lip oyster
A large oyster (variety of Pinctada maxima) used in some countries to produce South Sea cultured pearls; it produces a yellowish nacre, and pearls that typically range from off-white to rich, deep gold in colour.

Goniochromism
An optical phenomenon which causes the hue of the pearl to change colours depending upon the angle from which the pearl is viewed

Half-drilled
A pearl which has only been partly drilled, as for rings or stud earrings. These sell for more than those which are fully drilled. The best have a flawless domed side.

Hallmark
The term hallmark is often confused with branding, but it is not a branding. Hallmarking is a specific process of assaying precious metals and marking them as having passed a required standard. It is a guarantee of quality of content. Hallmarking dates, in England, from 1300 when Edward 1 brought in a requirement for standardisation of silver for coin and wrought pieces, which were to be marked with the leopard’s head mark to show they had passed assay.

Variations on the leopard’s head are still used today for sterling silver pieces marked at the London assay office, run by the Worshipful Company of Goldsmiths. Different marks are used to denote fine silver, and the various grades of gold, plus platinum and palladium. A mark will show when and in which office the item was assayed, plus what metal and who made the item. The mark is either struck to the metal (the origin of ‘making one’s mark’ as the maker can optionally still strike their own sponsor’s mark before assay or the mark can be struck by laser. All Pearlescence precious metals over the required minimum weight carries the London Assay office hallmark of owner Wendy Graham (Initials wmg in an oval cartouche).

Hyriopsis cumingi
The triangle shell is the shell used to culture most freshwater pearls in China Irradiation. Irradiation has differing effects from freshwater to salt water cultured pearls. The gamma rays do not affect the nacre layers of a salt water cultured pearl, but in fact darken the nucleus of the pearl. An irradiated salt water pearl appears to be grey or blue. The nacre of freshwater irradiated pearls, on the other hand, if affected by the gamma rays and can become very dark. Some of these freshwater treated pearls will also have an intense metallic sheen and iridescent orient over their
surface.

Kasumi
These are a sub-species of freshwater pearls grown only in Lake Kasumi-ga-Ura, some 40 miles northeast of Tokyo, Japan. They have a distinctive surface, like wrinkled satin. Kasumi like pearls are now being produced in China

Keishi or Keshi
Japanese word meaning “something as tiny as you can imagine”, such as a grain of sand; used originally for very tiny gems that resulted by accident as part of the culturing process; now used to refer to all-nacre baroque pearls produced when something goes wrong in the process of culturing so that the seeding nucleus is ejected from the half formed pearl. South Sea keshi pearls can be very large; Japanese keshi pearls can be minuscule. The shape ranges
from resembling a cornflake (so they are also called cornflake pearls) to something more like a slightly deflated balloon. They tend to have fabulous lustre.

Knots
Knots in the silk between pearls is a sign of quality in pearls. If there are no knots or the pearls are on beading wire and look stiff and without movement then they are not being assembled to show their best. The knots serve two purposes. Firstly the chances of losing all the pearls is minimised, only one or two maximum can be lost (Pearlescence always gets really annoyed at the scene in ‘Murder is Announced’ where the pearl necklace breaks and all the pearls shower onto the floor. Good for Miss Marple but very bad for pearls).

Secondly each knot acts as a hinge allowing the necklace or bracelet to flex. They stop the individual pearls packing closely. The picture shows a two strand necklace where the upper strand has been strung unknotted onto silk and the lower has been knotted. Never get strung pearls wet – this is not because the pearls will be harmed, it is very unlikely that just getting wet with water (either salt, fresh or swimming pool) will damage pearls after all, but the silk on which they are strung will rot in time especially the silk inside each pearl which is trapped and therefore takes much longer to dry. Please do wear your pearls all the time. Pearls need light oils to look their best and the oil in human skin is perfect. If you absolutely must wear your pearls in water then please let us know and we can re-string them on nylon. Play between the pearl and the knots. This is a sign that the silk may be stretching and it might be time to start thinking about getting them re-strung. We are happy to re-string pearls and will restring our own pearls at a reduced rate.

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This is my name, my phone number and my address, as a sender (written by FedEx)

We send your purchasing parcel via FedEx, we inform you the tracking number as soon as possible
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All About Pearls (Glossary A – C)

All About Pearls ( Glossary A – C )

wholesale pearlsA – AAA Grading system
Essence pearls are exceptional pearls, selected for highly metallic lustre, clean surface and shape, in that order. Usually only found by selecting in person. Probably under 1% of pearls will show the mirror metallic lustre we look for.

AAA: The highest-quality pearl, virtually flawless. The surface will have a very high lustre , not necessarily metallic, and at least 95% of the surface of each pearl is free of flaws. Any flaws are very small and hardly noticeable.

AA+ Nearly as good as AAA but perhaps slightly off round when rolled and a few more flaws although these will still only be visible on close inspection.

AA Average to good lustre, off round, blemishing to 20% of surface

A: This is the lowest jewellery-grade pearl, with a lower lustre and/or more than 25% of the surface showing defects. Probably a round pearl will be egg shaped, even from a distance Any website or other seller which talks about

AAAA+++ grade pearls is talking rubbish and this should be queried.

Tahitian pearls have a distinct and separate system, established by GIE Perles de Tahiti, and the Ministere de la Perliculture of Tahiti which grades from A (finest) to D ( poor) but to avoid confusion Miss Joaquim Pearls uses only the A to AAA gradings throughout the website.

Abalone blue pearls
Just being developed in New Zealand. The abalone produces a distinctive and stunningly iridescent blue pearl but is very hard to nucleate as its blood does not clot, so any damage will kill it.

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Akoya
A pearl from the akoya oyster (Pinctada Fucata Martensii). This is a salt water mollusc. Most cultured sea pearls are akoya pearls which are made with a bead nucleus, so that they usually have a good round shape. Big irregularities tend to be tails while less than perfect pearls have nacre with pits or convolutions. Good akoya pearls have a sharply reflective metallic lustre. Smaller (under 8mm) akoya pearls tend to come from China (although chinese production has dropped with the recession) while Japanese akoya pearl farmers are concentrating on producing larger high quality pearls (made-up necklaces marked Made In Japan may have been made with Chinese pearls if under 8mm) akoya pearls are harvested after only 9-16 months.

The problem is in obtaining pearls with sufficient nacre. Pearls with very thin nacre may even ‘blink’ which means that when rolled the nacre blinks to show patches where there is no nacre and you can see the nucleus. Below is a very bad example – the cream colour is nacre and the white is nucleus. Even when the nacre appears solid it can be very thin: peer closely and you can just about make out the thin line of the black nacre on the akoya pearl on the left (which split in half) The nacre on the pearl on the right is so thin the pearl is said to be blinking – if you roll it around it appears to blink, with sight of the nucleus.

Baroque
Baroque pearls are strictly all non-round pearls but the term is usually applied to pearls which are not round but which nevertheless have a good rounded surface all over. Freshwater pearls are most commonly baroque as freshwater pearls are mantle-tissue nucleated instead of bead nucleated. So round pearls are the exception, although more are being produced as techniques improve. The most valuable baroque pearls are South Sea and Tahitian pearls which are produced by Blacklipped and White-lipped oysters (Pinctada margaritifera, and the Pinctada maxima). Commercial baroque pearls tend to be bigger pearls – there is a balancing act for the pearl farmer between leaving the pearl in the mollusc with the chance of a big round pearl and the likelihood that the pearl will go out of round and become baroque and therefore less valuable

Bead Nucleation
All sea pearls are grown around a bead. It used to be that beads were not used in the production of most freshwater pearls (exceptions include coin pearls for example) However the last couple of years have seen the development of bead nucleation in freshwater pearls, producing second or third graft round pearls of stunning colour, lustre and shape. High quality bead nuked pearls are still exceptional and unusual and therefore very expensive, but can be up to 14mm. These freshwater pearls have been bead nucleated, and you can see the thick layer of nacre surrounding the nucleus

Biwa
Or sometimes biwi-A freshwater pearl grown in lake Biwi in Japan. Not in the present as the pearl farms were closed due to pollution. Now often applied to any stick pearl

Bleaching
White pearls are colour treated by bleaching. This applies to both Akoya and Freshwater pearls. Black-lipped Oyster Pinctada margaritifera This oyster produces the Tahitian black pearl

Blinking
Term to describe poor quality bead nucleated pearls where the nacre does not even fully cover the nucleus. When the strand is rolled the pearls look as if they are blinking.

Blister
A pearl that is attached to the inner surface of a mollusc shell

Button
Often rounded on one side and flat on the other. Sometimes also called a fastener pearl . Most often used to make stud earrings, because in larger sizes round pearls can be too proud of the earlobe.

Carat
Classic term to identify the amount of gold in metal. Different metals are added to gold to harden it and make it more durable. Expressed as a fraction of 24 parts so that 24ct is fine gold or pure gold, down to the lowest standard which is 9ct in the UK, usually 14ct elsewhere.

Circle pearls
No one knows exactly why some pearls develop circles. These can be bands of colour or grooves, as if the pearl has gently spun on its axis in the pearl sac. While circle pearls tend not to be the most expensive they are not as yet imitated and have stunning variety

Colour.
Natural freshwater pearls tend to be shades of white through to pale pinks and peaches and golds The intensity of the colour depends on the species and strain of host mollusc plus the farm water and food. Tahitian and South sea pearls are not usually dyed.

Colour Treatments
Many pearls are coloured treated as part of the processing between farm and retailer. There is however, now a trend towards completely natural colour untreated pearls. Silver nitrate and gamma radiation are two treatments. (see separate entries) and white bleached akoya pearls are often ‘pinked’ – delicate tinted to a faint pink overtone which softens the colour and is supposedly more flattering and desirable.

Coin
Usually a round flat pearl shaped like a coin, also used to describe fancy hearts, squares, lozenge and other shaped pearls

Conch Pearls
Rarest of the natural pearls, conch pearls look a bit like jelly beans. They are not nacreous but have a distinctive flame pattern on the surface. The colours range from orange, through yellow to pink

Cook Island Pearls
Specific group of south sea islands which produce their own distinctive pearls from Pinctada Margaritifera. The pearls show the same colours as Tahitian pearls but are softer looking in shades

Cortez Pearls
Very rare pearls produced by one farm in the Sea of Cortez, Mexico,from Concha Nácar, Pteria sterna, the rainbow lipped oyster. These pearls fluoresce red under UV light.

Cross
Cross can be diagonal or crucifix. Some cross pearls which also have nacre between the limbs have been sold as butterfly pearls

Cristaria plicata
The cockscomb pearl mussel was the mollusc originally used by the Chinese when they started to culture freshwater pearls. The pearls produced are known as rice crispie pearls because of their resemblance to the cereal

Cultured
A pearl formed after a human puts a bead nucleus or mantle tissue into a mollusc. Any farmed pearl is cultured. Any real pearl feels faintly gritty when rubbed gently on your teeth and the drill hole tends to be very small (usually 0.7mm)(because pearls are still often sold by weight)

Culturing Freshwater Pearls
In freshwater mussels, insertion of only mantle tissue is enough to trigger the making of a pearl sac and therefore pearl production. It used to be that beads were not used. However the last couple of years have seen the development of bead nucleation in freshwater pearls, producing second or third graft round pearls of stunning colour, lustre and shape. High quality bead nuked pearls are still exceptional and unusual and therefore very expensive, but can be up to 14mm. Even larger pearls are being produced with pearls nucleated with a lump of mud (!) these pearls, third graft, are of stunning lustre and a rather keishi appearance so far. When drilled the mud is drained away so that
the pearl is hollow and light in weight. However most freshwater cultured pearls are still solid pearl nacre, even pearls up to 15mm. This means that they are arguably more durable but the chances of non-perfect round shapes are higher

Since so many good quality white fake pearls are now available the trend is for natural colour pearls to remain untreated. Usually white freshwater pearls have to be bleached. There are many natural colours of freshwater pearls; pink, peach, purple, yellow, white, grey, brown, champagne and black. Only freshwater pearls are ever pink, peach and purple.. Black pearls are created by black oysters. The darker the colour is, the more valuable the pearl and black pearls with a little bit of green are the most precious.

Other colours are created artificially by dyeing or irradiating the pearls, or treating chemically. It is quite hard to tell with some colours whether or not a pearl has been treated (although a deep blue or hot pink pearl is never natural). Irradiated pearls are often silver/grey, blue, green, or gold to brown. Most dyed pearls are colourfast, and irradiated pearls won’t lose their colour, and are not radioactive.

While Salt water oysters will only manage to make one pearl each (which keeps up their scarcity and value) freshwater mussels are more obliging and will make 20 or more each. Some farms are developing their own strains of mussel, selecting for quality, while other farms will buy in their mussels ready nucleated. This careful breeding is producing more strongly coloured natural colour pearls. After harvest in China pearls go from individual farms to pearl factories where they are bleached to be white pearls, or otherwise coloured or processed, drilled and sorted, and assembled into strands.

Culturing Saltwater Pearls
Several distinct types of pearls grow in salt waters. Farming methods are pretty much the same for all of them
The process of growing sea pearls in oysters was discovered (or re-discovered as there are arguments about this) by Mikimoto in 1893. All pearls which grow in salt water start with baby oysters which are either artificially bred in a
hatchery or spawn naturally then are collected by placing various lures in the water to attract the spats as they are called. The baby oysters are grown on for two or more years until they are big enough to manage to accept a grafted bead nucleus.

With all sea pearls the pearl is grown around a nucleus – a starter bead plus a tiny fragment of mantle tissue which grows to form a pearl sac around the bead. As the mantle tissue is tissue for making nacre/shell it carries on doing this, secreting nacre on the inside of the sac and onto the bead. Mantle tissue makes the pearl sac because its job normally is to secrete the mother of pearl to make the smooth and lustrous lining of the oyster’s shell.

Early in the morning of the day an oyster will receive a nucleus, it is taken out of the water and then left for about half an hour, by which time it should have opened its shell a little. The shells are wedged open. Any unopen shells go back into the water to be left for another attempt in a few days Nucleating oysters is a skilled task – even opening the shell too far can kill the delicate creature. The bead-plus-mantle tissue scrap is inserted into an incision into the body of the oyster, either at its gonad or by the connective tissue. Remarkably having a bead stuck into its sex organ seems to make the oyster more active sexually rather than less!

A nucleus is a (usually) round bead made from shell and cut and polished into a smooth round -usually about 8mm in diameter for first grafting The oyster is secured in a clamping device in front of the operator and either the wooden wedge is left in place or a retractor which allows the shells to be forced further apart is inserted. If the oyster is opened too far it will die. The aim is for this process to take under a minute and it is reckoned that it takes a month at least for the oyster to recover.

The actual process is that the grafter, working through the tiny opening between the two halves of the shell, makes n incision of about a centimeter into the oyster’s gonad or into its connective tissue then places the mantle tissue and nucleus (dipped in water and held by a suction tool) into this slit. The two insertions must be touching, or a pearl sac will not form. Then the oyster is put back into the sea. There are various ways it is held but they all work to allow the oyster to feed happily and grow. No-one knows exactly why some grafts become great pearls and others don’t. It is probably a mixture and  combination of genetics, grafting skill, and growing conditions. Many farms keep a record to see who is the best grafter (!)

The implanted tissue forms a pearl sac around the nucleus and starts to secrete nacre. It will take between two and four years for the pearls to form. The tissue implant is only about 1mm square. It will form the pearl, which has no genetic relationship with the host mollusc. Nacre is mostly carbonated calcium. As long as the irritant is present the mollusc continues to add layers of nacre until a smooth lustrous pearl is formed.

Only one pearl per oyster can be produced. Sometimes oysters can be re-nucleated after harvesting to produce a bigger pearl with a bigger nucleating bead, or, if no bead is used a keishi pearl can be produced (think of the inside of an inflated then deflated balloon) Oysters are fairly fussy about their conditions and if forced to open too much they will die, as they will if they are out of the water too long, get too hot or too cold, if the water in which they live becomes too saline or not saline enough (this happens when a river floods and any oysters living in the estuary may well die because of the temporary dilution of salinity. It takes about 18 months to two years to grow tahitian and south sea pearls. Tahitian pearls are required by local law to be x-rayed and have a minimum nacre depth of 0.8mm all round. South sea pearls tend to have much thicker nacre than this.

There is some controversy about how long akoya pearls need to stay in the water. Some are harvested after only six months but these pearls can have gaps in their nacre so the bead is visible (they are said to ‘blink’ when rolled) and they will wear out quickly. But they will, of course, be very much cheaper. The pearls are cosseted. They will be cleaned several times to remove algae, vegetable growths and barnacles, and the farmer must keep an eye on the weather conditions – some akoya farms now monitor temperature and salinity and move the oysters if conditions are not ideal.

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IDENTIFICATION OF IRRADIATED SOUTH SEA CULTURED PEARLS USING ELECTRON SPIN RESONANCE SPECTROSCOPY

IDENTIFICATION OF IRRADIATED SOUTH SEA CULTURED PEARLS USING ELECTRON SPIN RESONANCE SPECTROSCOPY

wholesale pearlsIrradiated South Sea cultured pearls (SSCPs) from the Pinctada maxima mollusk typically show colors from light gray to silver. It is difficult to identify gamma-ray irradiation of SSCPs using standard gemological methods because of their thick nacre. Therefore, an advanced analytical technique such as electron spin resonance (ESR) spectroscopy is needed to detect the treatment.

ESR measurements of minute amounts of SSCP powders revealed the formation of CO2 – radicals, and the parameter known as the g-factor was
measured at 2.0015 ± 0.0005. Higher levels of CO2 – radicals were detected in the pearl nacre than in the nucleus. Therefore, the existence of CO2 – radicals is an indicator of irradiated SSCPs.

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Irradiation, dyeing, bleaching, and heat treatment are widely used methods to alter pearl color. Although most artificial colors are easily recognized, some resemble attractive colors that occur in nature (Elen, 2001; Li and Chen, 2001; Zachovay, 2005; Wang et al., 2006; “Better techniques improve brown pearls,” 2006; McClure et al., 2010).

Lower-quality freshwater and saltwater cultured pearls are regularly exposed to 60Co gamma-ray radiation in an attempt to simulate black pearls or enhance orient (Crowningshield, 1988; Li and Chen, 2002; O’Donoghue, 2006). In recent years, the irradiation process has been applied to not only Akoya cultured pearls and freshwater cultured pearls (FWCPs), but also to South Sea cultured pearls (SSCPs) (Choi et al., 2012). The irradiation-induced color change results from the darkening of the nucleus, caused by MnCO3 oxidation, as well as denatured damage to the
pearl’s conchiolin (Matsuda and Miyoshi, 1988). FWCPs have a higher abundance of proteinous components and manganese than saltwater pearls (Hatano and Ganno, 1962).

Gamma-ray irradiated SSCPs (figure 1) were first discovered in the Korean market in April 2011. At the March 2011 Hong Kong Jewelry Show, a Japanese trader reportedly sold a Korean counterpart irradiated SSCPs without disclosing the treatment. They were light gray or silver loose cultured pearls and beads 10–16 mm in size. While a cream, yellow, or black color is produced by a protein pigment in the nacre, a blue or silver color is caused by organic material between the nacre and nucleus (Komatsu, 1999; O’- Donoghue, 2006). Korean consumers typically prefer SSCPs with a silver color created by organic material. According to the research of Choi et al. (2012), gamma-ray irradiated SSCPs with colors ranging from white to cream turned light gray to silver, with the depth of color correlating with increasing irradiation dose. A dose of 0.5–1 kGy caused a light gray color, while a dose above 5 kGy produced a silver color.

For Akoya cultured pearls, with a typical nacre thickness of 0.2–0.6 mm, irradiation can be identified through standard gemological tests (Komatsu, 1999; O’Donoghue, 2006). But for SSCPs, which have a nacre thickness of roughly 1.5–3.0 mm, detecting irradiation is difficult with methods such as transmitted light, magnification, fluorescence reaction, and UV-Vis spectrometry (Choi et al., 2012). This study attempted to identify irradiated SSCPs using electron spin resonance (ESR) spectroscopy. This method, also known as electron paramagnetic resonance (EPR) spectroscopy, identifies the presence of unpaired electrons. Moreover, the study sought to minimize damage during examination by obtaining a minimal sample of powder from each cultured pearl.

MATERIALS AND METHODS

For the study, some 300 SSCPs weighing 6.55–18.05 ct (8.0–16.6 mm in diameter) with white to cream color were exposed to gamma-ray irradiation at room temperature. The irradiation was conducted at the 60Co facility of the KAERI (Korea Atomic Energy Research Institute) in Jeongeup, South Korea. The absorbed doses were set at 0.2, 0.4, 0.6, 0.8, 1, 5, and 100 kGy.

Inductively Coupled Plasma-Atomic Emission Spectrometer. Chemical composition analyses of the SSCPs were performed with an inductively coupled plasma–atomic emission spectrometer (ICP-AES, Varian Vista-PRO). The nacre, nucleus (bead), and conchiolin were separated and powdered, and 0.2 g of each powder was dissolved in a solution of 37%HCl (6 ml) and 65% HNO3 (2 ml). We tested the samples after 20 minutes at 200°C and after 10 minutes at the same temperature to obtain an average value. Electron Spin Resonance Spectroscopy. This study relied on electron spin resonance analysis to observe radicals produced by the irradiation process. The ESR spectrometer gauges the absorbed dose corresponding to the splitting energy of unpaired electrons in a magnetic
field. The technique can rapidly identify an irradiation- related signal from a small amount of sample in a few minutes. For this study, we collected at least 10 mg of SSCP powder from both the nacre and the nuclei of each cultured pearl. To determine if the ESR signals correlated with Mn2+, solid samples of FWCP, which contain more manganese than SSCPs, were irradiated with a 100 kGy dose.

Room-temperature ESR spectra were recorded using a JEOL FA-300 spectrometer with a manganese marker (MgO: Mn2+), using 9.8 GHz microwave frequency, 1 mW microwave power, a 1–2 G modulation amplitude, a 2 min sweep time, and a 0.03 s response time (figure 2).

Mn marker for ESR analysis. The g-factors of free radicals created by irradiation are approximately 2.00. For comparison, the “free electron” g-factor is 2.0023. Standard reference samples can be used to correct for any systematic errors in the measured magnetic field values and to verify the sensitivity of the system. Standard samples include DPPH (2.2-diphenyl-1-picryl-hydrazyl), TCNQ-Li (tetracyanoquino-dimethane Li saly), CaO:Mn2+, and MgO:Mn2+. The choice of standard sample used depends on what the user wants to determine. For example, DPPH is used to calculate gfactors, to monitor the sensitivity of the equipment, and to quantify spin concentrations. TCNQ-Li is used to find the g-factor. CaO:Mn2+, MgO:Mn2+, and Mn2+ are used to measure the g-factor and to correct magnetic field variations.

The g-factor of most standard samples is also located around 2.00. The Mn marker is shown with six Mn2+ signals; the third (2.034) and fourth (1.981) signals are used to correct magnetic field variations. Each signal has a regular interval from 2.00. From this property, the MgO:Mn2+ marker could be more suitable to measuring the g-factor than the alternative standard samples. The MgO:Mn2+ marker was supplied with the Jeol X-band spectrometer in the shape of a small rod that can be electromechanically inserted externally into the microwave cavity. When a sample and a Mn marker are measured simultaneously, the resulting ESR spectrum will contain signal contributions from both. It is easy to distinguish the ESR spectra of one from the other, since the Mn2+ signals have the opposite phase to that of the sample’s signal (i.e., the signal’s lineshape will appear to have been flipped across the baseline).
RESULTS AND DISCUSSION

The major element of a pearl is calcium. Chemical composition analysis of bead-cultured pearls using ICP-AES demonstrates that the nacre and the freshwater nucleus contain similar trace elements but vary in their composition. The nacre contains more Na, Mg, and Sr, while the nucleus has higher Mn and P contents (table 1).

After 60Co gamma-ray irradiation at a dose of 5 kGy, the SSCPs exhibited gray to silver coloration (figure 3). The interior of one of the irradiated pearls revealed a grayish brown to dark gray nucleus, along with an altered nacre color (figure 4). The irradiationinduced color change is chiefly attributed to the darkening of the nucleus (bead), which in turn darkens the nacre—especially in the thinner-skinned Akoya cultured pearls (Komatsu, 1999). As shown in this experiment, color change took place in the nacre as well.

Figure 5 shows that the concentration of radicals produced by irradiation exposure increases with the absorbed dose. Formerly undetected free radicals were observed after a low-dose radiation of 0.2 kGy. The g-factor was 2.0015 ± 0.0005, which agrees with that of CO2 – radicals (Wieser et al., 1985; Ikeya, 1993; Seletchi and Duliu, 2007). With higher absorbed doses, the CO2 – radical signal intensity further intensified. The identification of CO2 – radicals through ESR analysis thus serves as a way to distinguish irradiated cultured pearls.

Matsuda and Miyoshi (1988) reported that the irradiation – induced change of color is caused by manganese (Mn). They noted that MnCO3 in the nucleus (bead) turned into oxidations such as Mn3O4, Mn2O3, and Mn2O after irradiation. Their results are still cited in literature related to color change in irradiated pearls (e.g., Komatsu, 1999; Wada, 1999; McClure, 2010).

Yet existing mechanisms are insufficient to explain the alteration of pearl color by irradiation (Li and Chen, 2002). Based on the results of gamma-ray irradiation tests in this study, the authors believe that post-irradiation color change cannot solely be attributed to MnCO3 oxidation. Two factors support this hypothesis:

  1. After irradiation, the pearl nacre blackened to a similar extent as the nucleus (bead), even though it contains approximately 20 times less Mn (see figure 4 and table 1). Figure 6 is an ESR spectrum comparing untreated FWCP, irradiated (100 kGy) FWCP, and a Mn marker (MgO: Mn2+) attached to the JEOL equipment. The Mn marker consists of Mn2+ and shows six sharp peaks in the ESR spectrum (figure 6b). Before (figure 6a) and after (figure 6c) irradiation spectra of FWCPs (typical in the carbonate spectrum) do not match the positions of the Mn2+ signals. Nevertheless, a change was observed in the spectra before and after irradiation: the formation of CO2 – radicals between the third and fourth Mn2+ peaks (highlighted by the green circle in figure 6c). Because these results were the same among all SSCPs investigated in this study, peaks in the ESR spectrum are unrelated to Mn.2.CO2 – radicals appeared as irradiation doses increased and multiplied in proportion to the dose (figure 7). The intensity of CO2 – radicals was also proportional to the blackening of the pearl nucleus (bead). The CO3
  2. molecular ion in CaCO3 is easily ionized by radiation. Elementary defects induced by ionizing radiation are an electron center ( CO3- 3–) and a hole center (CO3–). While the CO3- 3– and CO3 – centers are stable at low temperatures, the electron center CO2 –, formed by irradiation, is an electron center similar but more stable than CO3- 3– (Ikeya, 1993). Additionally, we found that the color of nacre and nucleus had been bleached
    under incandescent light (approximately 50°C) for 30 days. The color changed by irradiation and heat (by light) is related to the color center. Therefore, the color change of the nacre and the blackening of the nucleus (bead) are believed to be related to color centers formed by CO2 – radicals. Choi et al. (2012) found that after irradiation, glutamic acid decreased 11.43% (from 3.5% to 3.1%), alanin 21.8% (from 22.5% to 21.8%), and histidine 43.75% (from 1.6% to 0.9%), according to amino acid analysis to examine the change of protein between aragonite platelets in pearl nacre. Hatano and Ganno (1962) found that gamma-ray irradiation destroyed 32% of the histidine, 16.6% of the methionine, 11% of the glutamic acid, and 9.3% of the proline in the
    protein of the FWCPs. The destruction of protein caused by irradiation can also alter the color of SSCPs.

CO2 – radicals at the absorbed irradiation dose of 0.2 kGy are barely visible in the nucleus sample but far more intense at doses above 0.4 kGy (figure 5, right). In particular, CO2 – radicals emerging after irradiation were better observed in the nacre than in the nucleus at the same absorbed dose (figure 5, left).

After normalizing the results of figure 5 to a nonirradiated spectrum (0 kGy, black line), the increased intensity of radicals was calculated by peak-to-peak height. The intensity of the CO2 – radical is stronger in the nacre than in the nucleus when irradiated with a dose above 0.4 kGy (figure 7).

Ikeya (1993) reported that Mg2+ ions might be accompanied by H2O molecules, leading to a rapid reduction in hydrated radicals. The saturation level of isotropic CO2 – also increases with the Mg/Ca ratio. Barabas et al. (1989) studied synthetic carbonate crystals doped with Mg2+ and observed the following:

  1. ESR spectra that displayed signals at the same spectroscopic properties as natural carbonates; and
  2. an increase of the g-factor signal with Mg concentration in the carbonate crystals. Mg also plays an important role in the formation of the crystal lattice of carbonates (Katz, 1973) and may enhance the formation of specific defects (Barabas et al., 1992). Lattice distortions caused by the incorporation of Mg2+ ions (Goldsmith and Graf,1958) may lead to CO2 – by creating larger interatomic distances (Barabas et al., 1992). In this context, thehigher abundance of CO2 – radicals in the nacre is thought to be related to the Mg/Ca ratio.

Considering the combined published observations on Mg2+ and CO2 – (Ikeya, 1993; Barabas et al., 1989, 1992; and Katz, 1973) it is likely that the saturation level of CO2 – rises proportionally with the Mg/Ca ratio in pearls of this study. As shown in table 1, the nacre and the nucleus (bead) contain 100 and 26 ppm of Mg, respectively. The nacre’s Mg/Ca ratio is approximately four times greater than that of the nucleus (bead). Mg, which is more abundant in the
nacre, therefore results in the preferential formation of CO2 – in the nacre rather than in the nucleus when exposed to the same absorbed radiation dose. This is consistent with the higher CO2 – ESR signal intensity observed in the nacre than in the nucleus (again, see figure 5). This suggests it is possible to identify an irradiated SSCP using ESR spectroscopy.

CONCLUSIONS

Identifying irradiated SSCPs through traditional gemological methods has been difficult, as their nacre is usually quite thick. But as this ESR study demonstrates, the separation of untreated pearls from irradiated pearls is possible. In doing so, an infinitesimal amount of sample was taken from the nacre in the form of powder. After irradiation, CO2
– radicals were formed, and their presence was confirmed using ESR spectroscopy. The amount of CO2 – radicals increased in proportion to the irradiation dose, and they were more observable in the nacre than in the nucleus
(bead). Until now, irradiation-induced color changes in pearls were thought to be due to the change of the MnCO3 oxidation number. But as this study notes, such color alteration is apparently related to an alteration caused by protein destruction rather than Mn, as well as color centers created by CO2 – radicals.

In Brief

  • Gamma-ray irradiation is routinely applied to South Sea cultured pearls (SSCPs), typically producing a light gray to silver color.
  • For SSCPs, which have a particularly thick nacre, detecting irradiation is difficult using methods such as transmitted light, magnification, fluorescence reaction, and UV-Vis spectrometry.
  • Electron spin resonance (ESR) spectroscopy rapidly identifies the presence of CO2 – radicals, whose concentration is proportional to the absorbed irradiation dose.

Articles source: Youngchool Kim, Hyunmin Choi, Bohyun Lee, and Ahmadjan Abduriyim – GEMS & GEMOLOGY, WINTER 2012
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Wholesale pearls for jewelry making : UPDATE ON THE IDENTIFICATION OF DYE TREATMENT IN YELLOW OR “GOLDEN” CULTURED PEARLS

Wholesale pearls for jewelry making : UPDATE ON THE IDENTIFICATION OF DYE TREATMENT IN YELLOW OR “GOLDEN” CULTURED PEARLS

wholesale pearls for jewelry makingDye treatments in yellow or “golden” cultured pearls have improved to the point that some samples show little surface evidence. In addition to routine gemological observations, analytical techniques such as UV-Vis reflectance and Raman photoluminescence (PL) spectroscopy are critical to identifying the treatment. This study demonstrated three indications of dye treatment: broad reflectance features between 410 and 450 nm, the lack of a reflectance feature at 350 nm in the UV-Vis spectra, and intense fluorescence in the visible spectrum under 514 nm wavelength laser excitation. These diagnostic features may be used independently, even when no visual evidence of a dye exists. (refference : wholesale pearls for jewelry making )

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Most dyed yellow or “golden” cultured pearls can be identified with routine microscopic observations. Dye residues usually accumulate within drill holes and surface blemishes, making them easy to detect with magnification. In some cases, long-wave UV fluorescence and UV-Vis reflectance spectrophotometry have been used to provide further evidence of dyeing (Elen, 2002; Qi et al., 2008; Chen et al., 2009).(refference : wholesale pearls beads )

In recent years, though, GIA has begun receiving more “golden” cultured pearls with a typical UV fluorescence or UV-Vis reflectance characteristics but no evidence of dye residue. As processing techniques continue to improve, the authors believe it is important to update the trade on the situation to make sure that current identification methods are up to par with the treatments. The term “golden” is used to describe mid- to light-tone cultured pearls with a strong saturation in the yellow and orangy yellow hues (Gemological Institute of America, 2000).(refference : wholesale pearls beads )

These cultured pearls are formed within Pinctada maxima (gold-lipped) oysters and have gained popularity over the years with the help of extensive marketing efforts by the industry (Shor, 2007; “The fabulous golden pearls of the Philippines…,” 2010). In the meantime, increasing amounts of dyed “golden” South Sea and freshwater cultured pearls (“Supplier warns trade against dyed golden,” 1998; Roskin, 2005) and, to a lesser extent, heat-treated “golden” products have also appeared on the market (Elen, 2001 and 2002).(refference : wholesale pearls beads )

Detecting the treatment remains an important consideration in pearl identification, and an ongoing research investigation at GIA aims to provide solutions to the issue. The present study focuses on the identification of eight sample groups of yellow or “golden” cultured pearl using routine gemological testing methods and advanced analytical techniques (figure 1). (refference : wholesale pearls beads )

Figure 1. These cultured pearls represent each of the eight sample groups. Top row: NSSP, NSSM, DSS, and DSS2. Bottom row: DSS3, DAK, DAK2, and DFW. Photo by Sood Oil (Judy) Chia.
Figure 1. These cultured pearls represent each of the eight sample groups. Top row: NSSP, NSSM, DSS, and DSS2. Bottom row: DSS3, DAK, DAK2, and DFW. Photo by Sood Oil (Judy) Chia.

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The known dyed samples exhibiting no traces of surface dye concentrations were singled out for analytical testing. The results suggest that advanced techniques such as UV-Vis reflectance and PL spectroscopy can detect the dye even when surface concentrations are absent. More than 100 naturally colored yellow cultured pearls were tested with the UV-Vis reflectance technique to provide additional reference datasets. Some of the latter were also tested with PL for the same purpose. Lastly, three heat-treated yellow cultured pearls were tested; their results are discussed briefly, since the sample size is minimal. (refference : wholesale pearls beads )

MATERIALS AND METHODS (refference : wholesale pearls for jewelry making )
A total of 69 yellow and “golden” cultured pearls ranging from 6.5 to 14 mm were studied. The eight sample groups consisted of:

  • 10 naturally colored South Sea cultured pearls from the Philippines (NSSP)
  • 8 naturally colored South Sea cultured pearls from Myanmar (NSSM)
  • 21 dyed South Sea cultured pearls, in three separate groups (DSS, DSS2, and DSS3)
  • 20 dyed akoya cultured pearls, in two separate groups (DAK and DAK2)
  • 10 dyed freshwater nonbead-cultured pearls (DFW)

These samples were obtained from reliable sources who provided information on the samples’ provenance. Real-time micro-radiography examination with a Faxitron CS-100-AC confirmed they were all cultured pearl products. Each sample was examined with a standard gemological microscope, and photomicrographs were taken using a Nikon SMZ 1500 stereo-microscope. Fluorescence reactions were observed in a darkened room using a conventional 5-watt long-wave (366 nm) UV lamp. UV-Vis reflectance spectra were obtained using a Perkin Elmer Lambda 950 UV-Vis spectrophotometer with an integrated sphere accessory. (refference : wholesale pearls beads )

Selected samples from each group were also tested with a Thermo Nicolet Nexus 670 FTIR spectrometer and a Renishaw inVia Raman microscope. The three heat-treated cultured pearls were obtained from a reliable source. In addition, more than 100 naturally colored yellow or “golden” South Sea cultured pearls (from Jewelmer) were tested using an Ocean Optics USB 2000+ UV-Vis spectrometer. This unit takes less than one minute to run a pearl sample, making it ideal for rapidly examining bulk quantities. Some of these cultured pearls were also tested with PL spectroscopy. A summary of the various sample groups and advanced testing techniques is provided in table 1. (refference : wholesale pearls beads )

RESULTS (refference : wholesale pearls for jewelry making )
Gemological Observations and UV Fluorescence. All cultured pearls exhibited light yellow, orangy yellow, yellow, or strong yellow bodycolors of uniform color distribution except the dyed samples from group DSS3, which showed distinctly uneven color distribution. Under magnification, concentrated dye features were observed in three additional dyed groups (DSS2, DAK2, and DFW), while the other two dyed groups (DSS and DAK) showed no evidence of surface treatment (figure 2). (refference : wholesale pearls beads )

Figure 2. These microscopic images show the surfaces and cross-sections of representative samples from groups NSSM, DSS (high-quality dyed), DSS2 (low-quality dyed), and DAK (high-quality dyed). Photos by Chunhui Zhou; magnified 10×–70×.
Figure 2. These microscopic images show the surfaces and cross-sections of representative samples from groups NSSM, DSS (high-quality dyed), DSS2 (low-quality dyed), and DAK (high-quality dyed). Photos by Chunhui Zhou; magnified 10×–70×.

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To make matters even more challenging, cultured pearls from the DSS group did not possess drill holes, which serve to enhance the diffusion of the dye material, suggesting that a different dyeing technique was applied to them. Representative samples from groups NSSM, DSS, DSS2, and DAK were cut in half to observe the color distribution throughout their cross-sections.(refference : wholesale pearls beads )

Typical concentric growth rings were noted on the nacre of the naturally colored sample, while the growth structures in the dyed cultured pearls were largely masked by the infiltration of dyes. The presence of a drill hole in the samples from DSS2 and DAK had caused the dye materials to diffuse into the bead used to culture the pearls. UV fluorescence generally followed the body-color of the sample. Naturally colored orangy yellow to strong yellow cultured pearls usually exhibited weak yellow fluorescence, while lighter yellow samples exhibited moderate to strong yellow fluorescence.(refference : wholesale pearls beads )

It is a challenging task, however, to accurately and consistently describe fluorescence color, since there is no reference for comparison. In this study, dyed samples also showed varying degrees of yellow or orangy yellow fluorescence, but not distinctive enough to consistently separate them from the naturally colored variety. Samples from DSS3 and DFW showed uneven color distribution due to dye concentrations on their surfaces. General observations and measurements are shown in table 2.(refference : wholesale pearls beads )

UV-Vis Reflectance Spectra. Within each group, UVVis reflectance properties were generally consistent. Naturally colored samples (NSSP and NSSM) showed decreasing reflectance toward the lower visible and long-wave UV range, with subtle local reflectance troughs at about 350 and 440 nm (figure 3). These reflectance troughs may be due to (but not equal to) absorptions at specific wavelengths. Cultured pearls from five of the dyed groups (DSS, DSS2, DSS3, DAK, and DAK2) all showed distinct reflectance characteristics within the same range, but with broader, more prominent, and sometimes shifted reflectance features between 410 and 450 nm, consistent with previous findings (Elen, 2002; Qi et al., 2008; Chen et al.,2009).(refference : wholesale pearls beads )

Some of the dyed cultured pearls (DSS, DAK, and DAK2) also lacked the 350 nm reflectance feature, while others (DSS2 and DSS3) showed a steeper slope between 430 and 480 nm than that of naturally colored samples (figure 4), also consistent with previous findings. Dyed freshwater cultured pearls showed reflectance patterns similar to those of the naturally colored samples within the lower visible range, but lacked the 350 nm reflectance feature. FTIR, Raman, and PL Spectroscopy Results. We performed infrared and Raman spectroscopy on representative samples from each of the eight groups. The FTIR spectra only showed the vibrational modes of aragonite, the major component of all pearls, dyed or naturally colored (figure 5). Raman spectroscopy was performed with both 514 and 830 nm lasers. The 830 nm laser gave much better peak resolution while the 514 nm laser (data not shown) registered significantly higher background fluorescence in the dyed and naturally colored samples.(refference : wholesale pearls beads )

To clearly visualize the fluorescence characteristics of these samples upon laser excitation, we performed PL measurements. These confirmed that most of the dyed cultured pearls fluoresced at much higher levels than naturally colored pearls—in a few cases, reduced power had to be used to prevent peak oversaturation—making it a useful tool in identifying some cases of dye treatment (figure 7). A more useful way to look at the data, though, is to compare the ratio between overall fluorescence intensity (600–700 nm) and the height of the main aragonite peak at 545 nm (i.e., the F/A ratio; figure 8). Dominant or significant aragonite peak intensities were observed in the spectra of naturally colored samples, with the F/A ratio consistently below 5. For dyed samples, the ratio varied more due to the different dye materials used, but they were more likely to have F/A ratios of at least 10.(refference : wholesale pearls beads )

Additional Reference Collection Data Results. In addition to the 18 reportedly naturally colored yellow samples, we examined more than 100 reportedly naturally colored yellow to orangy yellow cultured pearls of various saturations using UV-Vis reflectance and PL methods. These provided useful baselines for comparing unknown samples. The UV-Vis reflectance results of these naturally colored yellow samples showed consistent spectroscopic characteristics, similar to those observed in groups NSSP and NSSM (again, see figure 3). Low PL fluorescence signals (and F/A ratio) were also observed in all of the cultured pearls. Building and maintaining a spectral database from naturally colored yellow samples of various saturations (figure 9) is important for comparative analysis and identification of dye treatment.(refference : wholesale pearls beads )

Figure 9. Naturally colored cultured pearls generally show consistent UV-Vis reflectance characteristics and less-intense PL features, which may be useful in identifying unknown samples. Photo by Adirote Sripradist.
Figure 9. Naturally colored cultured pearls generally show consistent UV-Vis reflectance characteristics and less-intense PL features, which may be useful in identifying unknown samples. Photo by Adirote Sripradist.

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Heat-Treated Yellow Cultured Pearls. In addition to dye treatment, heat-treated yellow cultured pearls have been reported (Elen, 2001). The exact mechanism of color alteration is still unclear. One theory suggests that heating changes the amino acid compositions of conchiolin proteins, altering their physical and chemical properties (Akiyama, 1978). Another possibility is that heating proteins and sugars (found in conchiolin) at high temperature under intermediate moisture levels and alkaline conditions will promote Maillard reaction, resulting in a color change similar to the browning effect caused by heating many kinds of food.(refference : wholesale pearls beads )

The three reportedly heat-treated cultured pearls were tested using UV-Vis reflectance and PL spectroscopy. The UV-Vis spectra lacked the obvious broad reflectance pattern found in dyed samples, consistent with an earlier report (Elen, 2001) that their heat treatment did not involve any addition of dye materials. Yet the PL spectra showed extremely intense fluorescence, which could be useful in separating them from naturally colored samples. A brief summary of these results appears in box A.(refference : wholesale pearls beads )

DISCUSSION (refference : wholesale pearls for jewelry making )
The dyeing of cultured pearls has been a common practice for many years (Alexander, 1960; Liddicoat, 1962; Johnson and Koivula, 1999), and it can usually be detected through careful examination of the surface. In our study, four of the six groups of dyed yellow or “golden” samples could be detected through conventional microscopic observation. Concentrated dye residues and uneven color distribution provided definitive evidence. These products are usually treated after drilling, which was confirmed by the dye residue within and around the drill holes. The other two groups (DSS and DAK) had relatively clean surfaces, and even a trained gemologist would have difficulty in separating them from naturally colored samples. Cultured pearls from the DSS group were treated without the aid of drill holes, while samples from the DAK group were dyed either before or after drilling. If they were dyed after drilling, further treatment such as bleaching may have been used to lighten any color concentrations that accumulated near the drill holes.(refference : wholesale pearls beads )

All the yellow or “golden” cultured pearls showed decreasing reflectance in the violet/blue region of the visible spectrum, which corresponds with the color reflected, in accordance with complementary color theory and human color perception. But naturally colored samples displayed a gradual decrease in reflectance, with subtle local reflectance troughs at showed significant reflectance troughs between 410 and 450 nm. These distinct reflectance characteristics can be explained by the different reflectance properties of natural pigments and the predominantly single-component artificial dyes applied to the treated products, as well as the variable concentrations of either.(refference : wholesale pearls beads )

Interestingly, the origin of the golden color found in South Sea cultured pearls may also be derived from nano-composite structures of the nacre, as reported by Snow (2004), which helps further explain the different reflectance features between naturally colored and dyed cultured pearls. For the DFW group, no significant differences were found in the violet/blue region of the visible spectrum, in part because they contained less dye than the other groups. Some of the dyed groups also lacked the local reflectance trough at 350 nm, which occurs almost exclusively in cultured pearls with yellowish hues and may be attributed to a particular pigment. Although some previous studies have reported the presence of natural pigments in naturally colored freshwater, Tahitian, and Pteria species samples (Karampelas et al., 2007; Bersani and Lottici, 2010), our study found no obvious differences using either infrared or Raman spectroscopy. Low pigment or dye concentrations, the location of these materials inside nacre platelets, and strong signal interference by aragonite crystal structure of the pearls could all make it difficult to detect any pigment or dyes using Raman spectroscopy. Yet dyed cultured pearls generally show higher PL under 514 nm laser excitation, likely a consequence of the fluorescence characteristics of the particular dye(s) applied. The result agrees with earlier studies (Liu and Li, 2007; Chen et al., 2009).(refference : wholesale pearls beads )

CONCLUSIONS (refference : wholesale pearls for jewelry making )
While most dyed yellow or “golden” cultured pearls can still be detected with relative ease using magnification, some show very clean surfaces lacking any evidence of dye. We have demonstrated that these can be identified by nondestructive, advanced instrumental techniques such as UV-Vis reflectance and PL spectroscopy. Our study suggests three indications of dyeing: broad reflectance troughs between 410 and 450 nm, a lack of a reflectance feature at 350 nm, or intense fluorescence in the visible spectrum under 514 nm wavelength laser excitation. When testing cultured pearls using advanced instrumentation, comparative analysis between naturally colored and dyed samples is an important part of the identification process in certain cases.(refference : wholesale pearls beads )

GIA has collected sets of data from numerous naturally colored yellow or “golden” cultured pearls with varying degrees of saturation to use as references for comparison against the spectra of unknown samples. Further analysis of “golden” cultured pearls is needed due to the unlimited number of dye materials that can be used to treat off-color or low-grade goods.(refference : wholesale pearls beads )

Articles source: Chunhui Zhou, Artitaya Homkrajae, Joyce Wing Yan Ho, Akira Hyatt, and Nicholas Sturman – GEMS & GEMOLOGY, WINTER 2012 (refference : wholesale pearls beads )
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