Yael Designs Blog

  • All About Pearls: Non-Traditional Treatments

     

     

    South Sea Cultured Pearls - Courtesy of GIA

    The list of non-traditional treatments a cultured pearl might go through is a bit longer than the list of traditional ones, though in essence there are only four families of treatments: Maeshori, filling, clear or natural coating and coloring. In normal jewelry dictum, customers do not need to be informed of pre-treatments, processes and traditional treatments. Generally it is assumed that most of a given type of gem will go through these types of treatments and therefore it is unnecessary to reiterate something that is nearly immutable. Optimally, non-traditional treatments ought to be disclosed to the customer, but sometimes the buyer has not been informed either and so does not have the information to pass on. It is always good to be aware so that you can discern for yourself.

    The first is a family of treatments reputed to be performed on most pearls; but even though they are not traditional treatments since they are relatively new, they are generally not disclosed. Instead, they might be referred to as a pre-treatment, if they are mentioned at all. These are subtle treatments that happen soon after the pearls are harvested, often in conjunction with traditional treatments. These treatments are known as “Maeshori”, which seems to be a bit of a catch-all phrase that refers to some form of heat treatment of which there are several variants.  Generally each factory has its own preferred method of Maeshori, some versions of which include adding a coating to the exterior of the pearl. The goal is to tighten the nacre, often by pulling a little of the natural moisture out of the pearl. This closes or fills minute spaces giving a tighter smoother surface that reflects and refracts light better, resulting in a better luster. Depending on the skill of the technician, the nacre may become brittle and the luster may fade with time, some as quickly as just six months and progressing to dullness in a few years.

    One known form of Maeshori involves soaking the pearls in solutions including mineral salts, methyl alcohol or hydrogen peroxide and methyl alcohol. They are heated while soaking for anywhere between 30 minutes and 30 days. This method can be performed in junction with the bleaching process, and therefore claimed to simply be a part of the bleaching process, which is a traditional treatment. The goal is to swell the nacre platelets to close or fill the minute spaces.

    Another form simply exposes the pearls to hot dry air using equipment that resembles a fruit or nut dryer. This method dries and tightens the surface nacre, which decreases the number of minute spaces to improve luster.

     

    Baroque cultured pearl with partial nacre - Courtesy Paspaley/GIA

    Sometimes, a pearl’s nacre might not be sitting properly on the bead nucleus - there might be an air bubble between layers or the bead might be entirely loose within the nacre. In instances like this, an epoxy-like substance is inserted to stabilize the pearl and also sometimes to add weight.

     

    Pitted and blemished cultured pearls - Courtesy Robert Wan/GIA

    Some pearls are coated with lacquer.  There are several reasons for this. They may be used to stabilize a thin nacre, to protect the nacre, and to keep it from chipping. They are also used to improve luster in much the same way as wax and oils: by filling holes, crevices and cracks. The lacquer may also be dyed the same color as the pearl to camouflage surface features, even coloring, and make strands of pearls match. This lacquer wears off over time, revealing and often damaging the surface of the pearl it coated.

     

    Rows of dyed cultured pearls - Courtesy Valerie Power/GIA

    One of the last resort treatments a pearl will receive, and the treatment that most drastically changes the look of the original pearl, is to have its color changed entirely. There are many methods by which this is done. The least invasive, but most obvious is by lacquering a pearl with a darker or brighter color than is natural to that pearl. If a pearl is required to be lighter, it is normally left in bleach longer, often under heat to speed the process. Although changing a pearl’s color is considered non-traditional, because bleaching is a traditional method, bleaching pearls often falls under the “acceptable” purview.

    Dying is one of the most common methods to change the color of a pearl. Often the pearl is dyed any shade from a rainbow of colors and is very easy to spot because of the unnatural shades. But pearls can also be dyed to more realistic colors, mimicking more expensive types of pearls. These dyes color the nacre, not the bead, so carefully looking down the drill hole can reveal the pearl’s original color.

    One of the more common substances used to dye pearls is a solution of silver nitrate. This is similar to the silver salts that were used to darken photographs. When exposed to light, the solution decomposes and leaves a dark stain that dyes the pearl from brown to grey to black.

     

    Niobium metal treated cultured pearls - Courtesy JTM

    There are other means to change a pearl’s color as well. Heat or heat and pressure treatment can be used to turn white pearls golden to brown. Also common is irradiation. Gamma rays are used to deepen the color of a pearl. Interestingly, salt water and freshwater pearls react differently to gamma rays because the gamma rays affect magnesium which is only in the freshwater material. The majority of salt water pearls are nucleated with freshwater shell beads, so the pearl is darkened by the gamma rays darkening the bead nucleus. This means that only grey to silver can be achieved because of the interference of the paler nacre. Freshwater pearls are affected throughout by gamma rays, giving them much darker tones and often lending them a metallic to iridescent sheen that tends to look unnatural. Though, this iridescent sheen might come from another source: metal vapor deposition. The pearl is placed in a vacuum chamber and coated with Niobium, giving a metallic sheen similar to that of an oil slick on water.

    There is nothing wrong with buying treated pearls, so long as you know what you’re getting. They are often more delicate and have a shorter life-span, so additional care needs to be taken. And the more treatment the pearls have seen, the less expensive they should be. The best course of action? Be aware of what is out there, and know what you buy or buy from someone you trust.

  • All About Pearls: Traditional Treatments

     

     

    Baroque Freshwater Cultured Pearl and Diamond Earrings, Yael DesignsBaroque Freshwater Cultured Pearl and Diamond Coordinating Earrings, Yael Designs

    Cultured pearls are well known for their delicate natural beauty. With what seems like minimal effort a beautiful gem is birthed from a strange and slimy sea creature. But it isn’t quite that simple. There are several treatments cultured pearls undergo that are considered “traditional”. Sometimes these traditional treatments are instead referred to as “processes” for reasons of legality and ease.  And depending on the quality of the pearl, amongst other factors, there are several treatments that a cultured pearl may or may not undergo which are not considered “traditional”.

    Traditional treatments are those that have been practiced on a gem type for an unspecified “long” time. And because they are traditional and assumed to have been performed on most if not all gems of their type, they are generally not disclosed. There are many gems that undergo treatments, both traditional and not traditional.

     

    Linseed Oil for Traditional Treatment of Emeralds, photo by Cecile Raley DesignsLinseed Oil for Traditional Treatment of Emeralds, photo by Cecile Raley Designs

    Pliny the Elder lists some of the common treatments of his time as: foils, oiling, dyeing, and composite stones; though of these only oiling is considered a traditional treatment that does not need disclosing. The Papyrus Graecus Holmiensis, a document dating from circa 300AD contains many treatments that are old enough to be considered traditional, but no-one ought use and expect much in the way of success. One purported treatment is this: “Take the pieces of mother of pearl and put them into bitch’s milk. Put the cover upon the vessel and leave it there 2 days and 2 nights. Draw them out, as they lie there strung on asses’ hair, and observe whether they have become white. If not, put them in again until they become excellent in this respect. If you afterwards besmear a man with this he becomes leprous.”

     There are more recent treatments to whiten pearls and restore luster such as those contained in the Papyrus Graecus Holmiensis, and of equally dubious merit. This one comes from an Australian newspaper dating from 1911: “Procure a small loaf of brown bread, in which, before the loaf is baked, the pearls are laid, strung upon a silk thread; or they may be closely wrapped in a piece of gauze. The bread is then allowed to bake thoroughly but not to become brown. When the loaf is taken from the oven, it is allowed to cool, after which it is broken and the pearls removed.”

     

    Matched Cultured Pearls

    "Pinked" cultured pearls with still visible slight visual variation since pinking is not a heavy dye.

    There are three specific traditional treatments or processes that are used on many, though not necessarily all pearls, and to great effect. They are first cleaned in a concentrated water and salt mixture to clean off the pearl. They are then bleached. This fully cleans and removes any organic material that might still cling to the pearl. It also removes or greatly lessens dark spots to even the color and lightens the pearls to a more preferred, whiter shade. The second process most pearls undergo is “pinking”. This is a delicate pink dye that gives a pink overtone to the pearl, which is generally the preferred shade in Western countries. Sometimes a silvery dye is used for a silver overtone. Factories say that the bleaching and pinking, or other similar pale dyes, are done to improve the ability to match pearls and to create a larger number of cultured pearls that are of appealing enough shades to purchase, and that costs would be prohibitive otherwise.

     

    Polishing Machine filled with Walnut Chippings, photo by PearlescencePolishing Machine filled with Walnut Chippings, photo by Pearlescence

    The third process is to tumble the pearls with gentle abrasive material such as slivers of bamboo, walnut shell or vegetable grit, often in an oily medium such as bees wax or oils. The abrasive material smoothes bumps and minor scratches, while the wax or oils fill small pits and improves the look of the luster. However, the bees wax and/or oils are not permanent.

     

    Natural Pearl of which some of the Nacre layers have peeled awayNatural Pearl of which some of the Nacre layers have peeled away

    There is one more traditional treatment, but it is seldom used. In this treatment, any stained, dull or damaged layers of nacre are carefully peeled away. This treatment requires a highly skilled hand. It was much more commonly used on natural pearls as there was no worry of peeling the nacre off the bead nucleus entirely.

    Generally, those treatments that go under the heading of "traditional" are those that add to the beauty of the pearls, but are not detrimental to the pearl itself. There is no such guarantee with the non-traditional treatments, some of which may be performed in conjunction with traditional treatments. These can affect how well the pearls age over time. We will discuss them in our next blog post

    Baroque Freshwater Cultured Pearl and Diamond Pendant, Yael DesignsBaroque Freshwater Cultured Pearl and Diamond Pendant, Yael Designs

     

     

  • All About Pearls: Luster, Surface Quality and Matching

    Black Cultured Tahitian Pearl ringTahitian cultured pearl and diamond ring, Orb Collection, Yael Designs

    Of the seven factors on which pearls are judged, luster, surface quality and matching are those important but subtle differences that may not be immediately obvious unless they are lacking. These are the qualities that lift pearls to "fine" quality!

    Luster may be the most important of all the seven factors upon which pearls are judged. Luster is the magnificent luminosity which pearls are known for and judged by. Luster in pearls is caused by light traveling through translucent layers of nacre and reflecting back to the eye. The nacre's thickness, its degree of translucency and the arrangement of the overlapping nacre layers all contribute to luster.

     

    Golden cultured pearl and akoya cultured pearl, MikimotoAkoya and South Sea golden cultured pearl earcuff, Mikimoto

    However, the luster of South Sea and Tahitian cultured pearls should not be judged against the luster of Akoya cultured pearls because of the temperature of the regions they grow in. South Sea and Tahitian cultured pearls grow in much warmer climates than that of Akoyas. Oysters lay down nacre more quickly when the water is warmer, creating a softer, more satiny luster. Nacre deposited slowly tends to be more translucent than nacre deposited quickly, giving the pearl a more mirror-like luster. But no matter the region, cultured pearls are generally harvested during winter months when the water is coolest and the luster most pronounced. A pearl with excellent luster will show reflections that are bright, sharp and distinct.

    The quality of the nacre is very important for the quality of a pearl, affecting many, if not most factors. Translucency and layer uniformity affects luster. The number of nacre layers affects size, just like the rings of a tree do. And, of course, the way the nacre is laid down affects surface quality.

     

    Baroque Freshwater Cultured Pearl and Diamond Pendant, Yael DesignsBaroque Freshwater Cultured Pearl and Diamond Pendant, Yael Designs

    Surface quality, or characteristics, refers to the blemishes or irregularities on a pearl’s surface. Just like any natural gem, a pearl’s growth is imperfect, with variations in growth becoming visible on the surface. However, as pearls have minimal treatment, these variations have different looks and names than those found on gems such as: “wrinkle” –an irregular ridge or crease; “flat” –a flattened section that is generally too small to affect the basic shape of an otherwise spherical pearl; and “abrasion” – a series of scratches on the surface.

    Almost all pearls have surface irregularities that are visible to the naked eye. Pearls that are nearly spotless or contain only blemishes that are nearly invisible to the eye are very rare. But this feature in itself does not make for an expensive pearl; it is in combination with all the other factors upon which a pearl is priced and judged. However, if surface characteristics are numerous, and affect the durability of the pearl, they can severely depress its value. Minor characteristics would be those that are few in number or insignificant enough to be hidden by a drill-hole or mounting.

     

    seed pearl tassel earrings Yael DesignsSeed pearl, diamond and black diamond tassel earrings, Leone Collection, Yael Designs

    Matching is an interesting factor in that it applies not to a pearl but to a piece of jewelry, and there are multiple ways in which it might or might not apply to said jewelry. Matching does not apply to a single pearl. And some multiple pearl creations are intentionally mismatched. However, such a piece of jewelry must still have a harmonious and balanced design, which requires a different type of matching ability. To match pearls for a uniform motif, a sorter must begin with a huge quantity of pearls to end up with a well-matched group. It also requires a great deal of labor, time and skill.

    As illustrated by the seven factors that pearls are judged by, choosing a piece of pearl jewelry can be a very complex process. But the most important factor is whether you love it or not!

     

    Golden cultured pearl pendant, Yael DesignsGolden cultured pearl and diamond necklace, Orb Collection, Yael Designs

     

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  • All About Pearls: Nacre and Color

    Cultured pearl, turquoise and diamond earrings, Orb Collection

    South Sea cultured pearl, turquoise and diamond earrings, Orb Collection, Yael Designs

    The factors of size, shape, color, luster, surface quality, nacre and matching all have very strong effects on the look of a pearl and how well it will hold up to wear and tear over time. Nacre and color are just two of these seven factors that ought to be considered when choosing cultured pearls for yourself. Size and shape were discussed in our previous blog post, and we will be discussing luster, surface quality and matching in the next blog post.

    To the naked eye, pearls look like delicate smooth globes of soft light. But under magnification, it’s a different story. Pearls have a texture closer to fine grit sandpaper; which is why you can feel their texture against your teeth, and partially why a lightly textured substance such as fish scales and varnish makes such a good coating for imitation pearls.

     

    Electron microscopy image of a fractured surface of nacre, By Fabian Heinemann

    Electron microscopy image of a fractured surface of nacre, By Fabian Heinemann

    Under magnification, the two substances that compose nacre become visible. One is platelets of aragonite, a crystallized form of calcium carbonate, and the other is conchiolin, the binding agent that holds the platelets of aragonite together, rather like bricks held in place by cement. And, in fact, when viewed in cross-section, this is exactly what nacre looks like! Each layer is semi-transparent, allowing light to pass through them and create that soft glow that pearls are so well known and loved for. Nacre and mother-of-pearl are made of the same substance, but have different names dependent on where they are found.

    Growing time within the oyster strongly affects how much nacre forms on the pearl. And more nacre generally means better luster and that the cultured pearl will wear and last better. But the longer the cultured pearl is left in the oyster, the more likely it is to become off-round; and round is a very important shape for pearls. Growing time, generally 6 months to 6 years, is usually kept to an optimal length to maintain this round shape; usually between 6 months to 3 years. This is one of the reasons that natural pearls are favored over cultured pearls: Because they are entirely formed from nacre, unlike cultured pearls which are started from beads, they are said to have better luster and wear for generations if well cared for. But they are seldom round.

     

    Pinctada Maxima by Line1

    Pinctada Maxima shell, photo by Line1

    Color is another important and obvious factor upon which pearls are judged. Pearls come in a variety of colors. The strongest factor as to what color a pearl will form in is the color of the “lip” of the oyster – the color of the mother-of-pearl already there. The color of the lip of the oyster that donates mantle tissue during the nucleation process can also affect the color of the pearl, but usually, these are both the same breed of oyster with the same color lip. Color can also be affected by any pollutants in the water.

     

    Baroque freshwater cultured pearl and diamond necklace

    Baroque freshwater cultured pearl and diamond one-of-a-kind pendant, Yael Designs

    It is more difficult to breed for certain colors of freshwater cultured pearls than it is for salt water cultured pearls because many of the mussels used to grow pearls have lips of multiple colors. Also, there are some pearl farmers who are experimenting with adding small amounts of "pollutants" directly into the mussels to see what color these chemicals influence the cultured pearls into becoming.

     

    Freshwater cultured pearl and diamond necklace, Custom Collection

    Freshwater cultured pearl and diamond pendant, Custom Collection, Yael Designs

    But body color is only the tip of the color iceberg for pearls. Some pearls also have overtone and/or orient. Overtone is defined as "one or more translucent colors that lie over a pearl's body color". It is believed that overtone might be caused by diffraction of light around the edges where nacre crystals overlap. These pearls have an additional glow of rose, green, blue, etc. over their main color. Rose is the most prized for Akoya grown cultured pearls. On dark green-grey Tahitian cultured pearls, the addition of rose to purple overtones create the prized "peacock" color.

     

    Tahitian cultured pearl and diamond ring, Orb Collection

    Tahitian cultured pearl and diamond ring, Orb Collection, Yael Designs

    In our next blog, we'll touch on the last three major concerns when choosing out a pearl: luster, surface quality and matching.

     

     

  • All About Pearls: Size and Shape

    custom collection, Yael DesignsGolden South Sea cultured pearl, yellow and white diamond pendant, Custom Collection, Yael Designs

    Just like diamonds, pearls have set standards by which they are judged. These factors are: size, shape, color, luster, surface quality, nacre and matching.

    Leone Collection, Yael DesignsSeed Pearl, black and white diamond tassel necklace, Leone Collection, Yael Designs

    Size is a relatively straightforward consideration. There are two main types of cultured saltwater pearls: Akoya, and South Sea and Tahitian. Because of Mikimoto’s influence, cultured Akoya pearls are the most commonly known. These were the type of oysters the pearls of which Mikimoto worked with and marketed. Cultured pearls from these oysters typically range in size from 2mm to 10mm. South Sea and Tahitian cultured pearls are grown in a species of oyster that is larger than Akoya. These oysters; therefore, are capable of growing larger cultured pearls, ranging in size from 8mm to 18mm. Interestingly, cultured pearls are sold by pearl farmers to dealers by carat weight, but sold to their final owners using millimeter measurements.

    The size of Akoya pearls should not be judged against the size of South Sea and Tahitian pearls because their size ranges and therefore their rarity at different sizes are not the same. All other things being equal, a 10mm Akoya cultured pearl is worth more than a 10mm South Sea cultured pearl because the Akoya is rarer than the South Sea at that size.

     

    Orb Pearl Collection, Yael DesignsOval-shape golden South Sea cultured pearl and diamond earrings, Orb Pearl Collection, Yael Designs

    As mentioned in our previous blog, round is a rare shape for natural pearls. The process of culturing pearls has made round pearls “The” shape. This is because salt water oysters can be nucleated with round beads, making it more likely that the finished product will be round. But because these are naturally formed gems, even with the round bead, their shapes still vary. Round is the most popular shape, followed by drop or teardrop. There are many other shapes besides, such as near-round, oval, button, baroque (which refers to an irregular shape) and semi-baroque. There are additional names for fancy shapes, but these cover the basics.

     

    Baroque Freshwater Cultured Pearl and Diamond Pendant, Yael DesignsBaroque freshwater cultured pearl and diamond pendant, Yael Designs

    Freshwater mussels are traditionally unable to be nucleated with beads as they have a high rejection and death rate, so traditionally have been nucleated with only a piece of mantle tissue from a donor mussel. However, freshwater cultured pearl farmers have been experimenting with crossbreeding mussels so that they can accept round beads as well. One reason for this is that cultured pearls nucleated with beads are often heavier than those grown without; and because pearl farmers sell by weight and not size, this factor alone increases their cultured pearls' prices. However, this has led to amazing innovation in the field. One of the most exciting new freshwater cultured pearls types to come out in recent years is called the Edison Pearl, and the farmers of these cultured pearls have managed to achieved a nearly perfectly round shape consistently. But there are also wildly popular shapes such as the fireball, which is a round shape with a wing of nacre trailing behind like a comet; and the Kasumiga or ripple cultured pearls which have a textured, rippled surface. Non-round freshwater cultured pearls have many names dependant on what they look like including: rice krispy, potato, cross, biwa, coin and bar.

     

    Baroque Freshwater Cultured Pearl and Diamond Pendant, Yael DesignsBaroque Freshwater cultured pearl and diamond pendant, Yael Designs

    What you have to look forward to in our next blog: nacre and color.

     

     

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