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Glossary Terms | Dahlia

A B C D E F G H I K L M N O P Q R S T U

A
Abalone Pearl: A natural pearl cultivated from an abalone, which is a marine gastropod of the genus Haliotis having an ear-shaped shell with a row of holes along the outer edge. Blister pearls, mabe pearls, and some semi-round pearls are also cultured in these mollusks, although most abalone pearls are natural. The colorful pearly interior of the shell is often used for jewelry.

A.G.S.: The American Gem Society, or A.G.S., is recognized as one of the top gemstone grading organizations. The A.G.S. has developed a commercial cut grading system that has been rapidly gaining popularity and acceptance in the valuation of diamonds.

Appraisals: Any appraiser should hold a diploma as a gemologist. All appraisals should identify the type of stones and metals, measurements and weights of stones, listing of color, clarity, cut quality blemishes and treatments, type of settings for jewelry.

Akoya Pearl: See Oysters.


B
Baguettes: A rectangular cut stone with squared corners.

Bar setting: A variation on the channel setting, usually used for wedding bands or designer rings. In the bar setting, thin metal bars are placed between each gemstone on a band to hold them securely in place. This design protects the girdle of the gemstones, holds them more securely than a prong setting, and offers a smooth, sleek appearance. Bar and channel settings typically cost more than prong settings.

Baroque Pearl: A trade term for any pearl, cultured or natural, that has an uneven and free form shape.

Bezel setting: Holds a diamond or gemstone in place at the girdle by a thin strip of metal that is soldered onto the band. The bezel setting can either create a smooth, flush, appearance, or leave the gem's crown exposed for extra drama. The bezel is also designed to allow maximum light shine through the stone from the bottom, so you get the most protection while still showcasing the brilliance of the stone.

Biwa Pearl: Originally, this term referred to a cultured freshwater pearl from Lake Biwa, a large lake near Kyoto, in Japan. However, the U.S. Federal Trade Commission has extended the use of this term to any pearl cultivated from Japanese freshwater mussels.

Blemish: Any flaw, spot, scratch or cut that appears on the surface of a gemstone. Blemishes for pearls can include spots, bumps, pits, holes, cracks, chips, wrinkles and dull spots. Blemishes fall into two categories, damaging blemishes and non-damaging blemishes. Non-damaging blemishes include spots, bumps, pits and wrinkles. These types of blemishes do not affect the durability of a pearl but will affect the price. Damaging blemishes, however, such as cracks, holes and chips will only get larger over time and wear and can seriously affect the durability and value of a pearl.

Brilliance: The amount of light allowed reflected from inside the gemstone based on the quality of its cut.

Button: A dome-shaped pearl with a flat bottom.


C
Cabochon: A gemstone cut that creates a dome shape. This cut is often seen in opal, turquoise, and star rubies and sapphires.

Carats: Metric system of measurement for gemstones where one carat equals 200 milligrams, or 0.2 grams. Each carat is divided into 100 points, so a 75 point stone is ¾ of 1 carat, a 50 point is ½ carat, etc. Note that gemstones can only be weighed for certification when un-mounted.

Certificate: The official grading report for gemstones. Certificates can come from any of the major gemstone laboratories, the best being the G.I.A. and the A.G.S. The certificate will list all the major quality factors. For pearls, most labs will x-ray the pearl to determine if it is natural or cultured.

Channel setting: Two strips of metal hold the gemstone in place by creating a channel for the stone. Unlike the bar setting, channel set stones have no metal between the stones. This is a great setting for active people as the stones are protected from snags and bumps.

Central Gem Laboratory: A lab in Japan that specializes in pearl evaluation and reports.

Chalky luster: A term for defining bad luster in pearls. It usually indicates thin nacre, so it would be better not to buy them because chalky pearls are poor quality and may chip.

Circles: Concentric rings formed on the surface of a pearl that are concave in appearance. If circles are apparent on more than 1/3 of a pearl's surface then the term "circle pearl" is applied to describe the shape of a pearl. If less than 1/3 of a pearl's surface is covered by circles, then the circle is considered a blemish and not a shape description.

Clean: A term used to describe the absence or relative absence of any visible blemishes on the surface of a pearl.

Color: Different varieties of mollusks produce specific natural colors. Although color is usually a preference of the wearer and not an indicator of quality, generally creamy/yellow hues are less valuable than other pearl colors. Our Freshwater pearls develop into a wider range of colors than any other type of pearls. Colors include a range of light and intense deep colors such as white, pink, peach, tangerine, lavender, plum, cocoa, and more.

Conch Pearl: Pink coral pearls produced by a conch, which is a saltwater mollusk from tropical waters.

Conchiolin: Organic matter layed out in thin sheets, on the external side of the shell. Also a component of nacre.

Cultured Pearl: A pearl grown in a mollusk that has been surgically implanted a hard bead nucleus or soft tissue nucleus at its center by human intervention. Due to the scarcity of natural pearls (approximately one in every 10,000 mollusks), most pearls today are cultured pearls.


D
Dispersion: Or "fire", the rainbow colors seen in a properly cut gemstone.


E
E.G.L.: European Gemological Laboratory. An internationally respected organization that provides independent quality grading for diamonds.

Emerald cut: A step cut gemstone that can be rectangular, square, or even triangular, where the corners have been cut off for protection and easier prong setting.

Enhancements: The only enhancements that are accepted in the gemstone industry are those that result in permanent color improvement. All enhancements should be clearly stated on the bill of sale.


F
Facets: The flat, polished, cut surfaces or planes of a gemstone. Each cut is made with the proportion of the entire stone in mind.

Freshwater Pearl: A pearl found in a freshwater mollusk usually inhabiting a lake, river or pond. Freshwater cultured pearls are from the mussel Hyriopsis cumingii and range from 2 ?18mm. Colors include white, lavender, peach, pink, mocha, and many others.


G
G.I.A.: The Gemological Institute of America. A non-profit organization specializing in grading diamonds and gemstones and recognized as the preeminent laboratory for impartial value grading.

Girdle: The narrow rim around a gemstone. The girdle is measured as the largest diameter of the stone.

Girdle width: The proportion of the girdle to the rest of the stone. Too thin a girdle leaves the stone susceptible to cracks and breakage, while a girdle too thick will have reduced brilliance and fire.

Gold: The most malleable of precious metals, gold will not corrode, tarnish or rust.

Gold filled: Any metal covered by a thin layer of gold. The layer must be at least 10k gold and 1/20th of the total weight of the piece.

Gold plate: Essentially the same as gold filled, except the gold content can be less than 1/20th the total weight.

Grafting: Also called nucleation or implantation, grafting is the human insertion of either a hard bead nucleus or soft mantle tissue into either the body of a mollusk or the mantle tissue of a mollusk. The nucleus or mantle tissue serves as a "seed" or "irritant" to produce a cultured pearl. A technician inserts into the gonad (mollusk's reproductive gland) a nucleus and mantle-tissue graft. The process takes one or two minutes. In the following weeks, proliferating epithelial cells will form the pearl-sack. Then concentric layers of nacre will be secreted around the nucleus and cover it.


H
Heat treatments: Almost all rubies and sapphires on today's market have been heat treated for color enhancement. This is a permanent treatment, and therefore totally accepted in the trade.


I
I.G.L.: The Independent Gemological Laboratories Inc., recognized as a reputable resource for grading gemstones.

Imitation Pearl: Simulated pearls made by humans or machines. Imitation pearls are usually either too heavy (inside is filled with glass) or too light (inside is plastic).

Inclusions: Any and all internal flaws naturally occurring in gemstones.

Irritant: The bead nucleus, tissue implant, or other substance, implanted into mollusks in order to produce pearls.


K
Karat: The standard measure of gold purity wherein one karat is 1/24th pure, meaning 24 k gold is pure gold.

Keshii Pearl: Means "Poppy seed" in Japanese. A Keshii pearl is a non-nucleated pearl, which forms as an accidental offshoot of the cultivating process and is therefore not considered natural. Keshii pearls can be as small as 1 mm and as large as 10 mm in size.


L
Lab-grown stones: Any gemstone that is simulated in the lab using the same, or similar, properties found in the natural stones. These simulants are not considered imitations, but they are not natural.

Lacquer coating pearls: Used to create a lustrous shine, but it wears off quickly. Pearlessence, a fish-scale recipe, provides better luster and lasts a little longer, however, both treatments should be fully disclosed.

Layer: One layer of nacre = 1 micron approximately. The Polynesian Pinctada Margaritifera oyster secretes 3 or 4 concentric layers a day. In two years, the layer will be up to 2.5mm thick, whereas the Akoya oyster will only secrete 1 mm.

Loupe: The magnifying tool used to examine gemstones and jewelry, typically to 10X magnification.

Luster: Considered the radiance or depth of inner light refraction of a pearl and determined by the quality of the nacre coating. Luster is created by tiny crystals of nacre built up over the irritant. Natural pearls tend to have thicker nacre than cultured pearls, hence deeper luster. Dahlia pearls have thicker nacre than most other cultured pearls so our luster is very high.


M
Mabe Pearl: Also referred to as blister pearls, mabe pearls are half spherical cultured pearls formed on the inner shell of a mollusk and instead of in its body. Mabe pearls are created by attaching a plastic hemisphere onto the inside of a mollusk's shell. Once the hemispherical nucleus is covered with enough nacre, the pearl is sliced from the inner shell, the bead taken out, and the hollow filled with a substance such as epoxy resin and backed by a mother-of-pearl plate. These pearls are fairly inexpensive, but fragile.

Make: The term for proportions and finish of a cut gemstone. For pearls, the make relates to the match of pearls, quality of drilling and stringing of strands.

Mantle tissue: The thin tissue membrane that attaches a mollusk to its inner shell. Small pieces of mantle tissue are inserted next to hard bead shell nuclei to help cultured pearls grow in saltwater oysters, whereas pieces of soft mantle tissue are used in many freshwater mussels to grow cultured pearls. The mantle tissue disintegrates thus creating an all nacre pearl.

Matching: The process of matching pearls in terms of luster, surface, shape, color, and size to create a necklace or other piece of pearl jewelry.

Millimeter: A metric measurement of length used to determine a pearl's size. A millimeter is expressed as "mm," whereby one "mm" equals 1/25 of an inch. The millimeter is also used to measure gemstones other than diamonds below ½ carat.

Mohs Scale: The scale that determines the relative hardness of minerals. Developed by Friedrich Mohs, the scale uses a scratch test and ranks minerals soft to hard from 1-10.

Momme: A Japanese weight measurement used for pearls. One momme equals 3.75 grams or 18.75 carats.

Mounting: The method of holding gemstones in place in jewelry. Prongs, channels, etc. are mountings.

Mussel: Approximately 350 species of freshwater pearl mussels can produce pearls. Freshwater pearl mussels, from families Unionidae and Margaritiferidae, produce nacreous pearls which are lustrous and colorful. The greatest diversity of the species is in the Mississippi River, but these mussel shells provide the round bead nuclei used for perliculture in Japan, China and Australia.

  • Hyriopsis cumingii (commonly called Triangleshell Pearl Mussel): The most common cultured freshwater mussels are grown in the waters of Japan or China. These pearls generally range in size from 2 mm to 18 mm and range in color from white, cream, gold, silver, pink, rose, lavender, plum, tangerine, and mocha shades.
  • Megalonaias nervosa (commonly called Washboard Pearl Mussel): Historical source for buttons, and the major source of pearl nuclei from the United States.


N
Nacre: (nay-ker) A calcium carbonate-based crystalline substance secreted by mollusks to form mother-of-pearl, pearls, and cultured pearls. Nacre secretion by a mollusk is usually a defense mechanism triggered by the intrusion of a foreign object into the body of an oyster. Thicker nacre translates into a more durable pearl. Natural pearls are all nacre, whereas most cultured pearls have a bead nucleus in the center. The chemical composition of Nacre is:

  • 90% of calcium carbonate crystals (aragonite);
  • 5% of organic protein (conchiolin) that binds the aragonite crystals together;
  • 2% of water;
  • Sodium, magnesium, strontium.

Natural: Any pearl that is not cultured. Any gemstone that has not been color or clarity enhanced.

Needles: Long, thin, inclusions in gemstones caused by gas within the crystal.

Nucleus: Typically a small, round piece of polished shell from an American freshwater mussel used as an irritant or core in all saltwater cultured pearl production. The nucleus is 5 to 9 mm in diameter for a single graft, and 10 to 11 mm for an over-graft (when the mollusk is grafted again). In freshwater cultured pearl production, a nucleus is usually a small piece of soft mantle tissue from another freshwater mussel.

Nucleation: See grafting.


O
Off-center culet: A major problem in gemstone cutting. An off-center culet seriously affects the symmetry of a stone.

Oiling: A common procedure for gemstone color enhancement. The treatment is not permanent and should be disclosed at point of purchase.

Opaque: A descriptive term for gemstones that are so clouded by flaws that they cannot be considered at all transparent.

Oval: A cut shape for gemstones.

Overtone: The hint of secondary color found in pearls that is typically pink, green, blue and silver.

Oyster: Although 70 species of oysters can produce pearls, most of them belong to the Pinctada family. Below are the three most common oyster types.

  • Pinctada fucata or Pinctada martens (commonly called Akoya Pearl Oyster): Akoya cultured pearls-producing saltwater mollusks grown in the cooler waters of Japan or China. Akoya pearls generally range in size from 2 mm to 10 mm and range in color from white, rose, or cream shades.
  • Pinctada maxima (commonly called Silver- or Golden-lipped Pearl Oyster): The world's largest pearl oysters found in the waters around Australia, Indonesia, the Philippines and Japan. Colors include silver-white, pink, cream, and gold. These oysters grow in excess of 12 inches in length and can produce a wide range of South Sea cultured pearls in sizes from 8 mm to over 22 mm;
  • Pinctada margaritifera (commonly called Black-lipped Pearl Oyster): Saltwater mollusks grown in French Polynesia that produce Tahitian or "black" cultured pearls. Considered as adult at 3 years old, it has a diameter of 10 to 18 cm large. Some of these Black-lipped oysters can weigh up to 5 kg (11 lbs.), live 30 years and reach 30 cm (12 inches) in diameter.


P
Pave setting: Many small gemstones placed in tapered holes creating a "paved" appearance.

Pavilion: The bottom of a faceted gemstone, from the girdle to the culet.

Pavilion depth: Along with crown height, pavilion depth determines the overall proportion and symmetry of a gemstone cut.

Pear-shaped: A pearl that grows round on one end and tapers to a smaller top. Also a cut shape for gemstones.

Pearlessence: A substance of ground fish scales and lacquer used to make imitation pearls, or to coat low-quality pearls.

Point: A unit of weight measurement for gemstones. 0.01 carats is 1 point. 1 carat is 100 points.

Platinum: A precious metal that is far harder than gold. It is tarnish resistant and hypo-allergenic.

Princess cut: Square cut, brilliant style, gemstone.

Prong setting: A very popular ring setting style, common in engagement rings, where metal prongs are bent around the girdle of the gemstone to hold it securely in place, allowing maximum light to pass through.


Q
Quench crackling: A treatment performed on synthetic gemstones where they are heated and then dunked in cold water to produce natural looking flaws.


R
Reproduction: Having both male and female sex organs, the pearl oyster is a hermaphrodite. Depending on its age and surrounding water conditions, the oyster's sex may change. They release sperm and ovules in the water. Eggs are transformed into larvae, then into seed-oysters (or spats). Spat collecting is located either in areas where many wild adult oysters live, or in a pearl farm. A spat collector is made from bush branches or synthetic materials, on which seed-oysters will fix. Within 2 or 3 years, oysters will be old enough to be grafted. The reproductive organs are functional for only a short period each year during the five months from October to February.

Round brilliant: The standard round cut gemstone.

Roundness: Pearls are graded by their roundness: round, mostly round, slightly off-round, and off-round.


S
Seed pearl: A natural pearl less than 2 millimeters in diameter.

Shape: A quality evaluation category used to describe the shape of a pearl. The most valuable pearls are round. However, other shapes of pearls include off-round, drop, oval, button, semi-baroque and baroque. Freshwater cultured pearls are grown in all of those shapes as well as stick, square, cross and coin shapes.

Size: A quality and price evaluation category used to describe the size of a cultured pearl. Size descriptions are expressed in millimeter and measured by the diameter of a pearl. Typically, all other factors being equal, a larger cultured pearl is worth more than a smaller one. In fact, the value of a cultured pearl may double for every 0.5mm diameter increase.

Sorting: The process of sorting pearls before matching and jewelry assembly to separate pearls by luster, surface, shape, color and size. Each pearl is handled hundreds of times during the sorting and matching process.

South Sea cultured pearl: See Oysters.

Surface: A quality evaluation of the amount of blemishes on a pearl, ranging from clean to heavily blemished.

Synthetic: Any gemstone grown in a lab. They are "real" gemstones, but they are not "real" diamonds, rubies, etc.


T
Table: The largest facet on a gemstone. The table is on top of the crown and allows refracted light to escape, creating brilliance.

Table size: Most jewelers agree the table should be between 53% and 67% of the girdle diameter. A table percentage too large or small greatly effects sparkle.

Table percentage: The diameter of the gemstone divided by the size of the table.

Tahitian pearls: See Oysters.


U
Ultrasonic: A cleaning machine for gemstones and jewelry that blasts dirt away with ultrasonic waves. But cannot be used on all types of gemstones such as pearls. Be sure to consult a professional jeweler before cleaning any jewelry.

Uniformity: The grading system for defining how well pearls match on a strand. They can be excellent, good or fair.

Uniondae Hyriopsis Schlegeli: Most common freshwater mussel produces a pearl with thick nacre and bright luster. These pearls come in a wide variety of colors ranging from plum, lavender, peach, apricot, curry, red pepper, cinnamon, celery and sage.

 

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