- Introduction
- Cut
- Clarity
- Color
- Carat Weight
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Diamond is the ultimate gemstone, having few weaknesses and many strengths. It is well known that Diamond is the hardest substance found in nature, but few people realize that Diamond is four times harder than the next hardest natural mineral, corundum (sapphire and ruby). But even as hard as it is, it is not impervious. Diamond has four directions of cleavage, meaning that if it receives a sharp blow in one of these directions it will cleave, or split. A skilled diamond setter and/or jeweler will prevent any of these directions from being in a position to be struck while mounted in a jewelry piece.
As a gemstone, Diamond's single flaw (perfect cleavage) is far outdistanced by the sum of its positive qualities. It has a broad color range, high refraction, high dispersion or fire, very low reactivity to chemicals, rarity, and of course, extreme hardness and durability. Diamond is the April Birthstone.
In terms of it's physical properties, diamond is the ultimate mineral in several ways: |
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Hardness |
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Diamond is a perfect "10", defining the top of the hardness scale.
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Clarity |
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Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) than is any other solid or liquid substance - nothing else even comes close.
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Thermal Conductivity |
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Diamond conducts heat better than anything - five times better than the second best element, Silver!
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Melting Point |
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Diamond has the highest melting point (3820 degrees Kelvin)
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Lattice Density |
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The atoms of Diamond are packed closer together than are the atoms of any other substance.
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For grading purposes, the word "cut" means the proportions and finish—or make—of a polished diamond. Proportions are the angles and relative measurements of a polished gem's facets and the relationships between them. Finish is the quality of the polish and the precision or symmetry of the cut. These factors, along with the thickness of the girdle, affect a diamond's overall cut grade.
A diamond is a tiny set of mirrors that interact with light to create the gem's face-up appearance. Contributing to that interaction are the diamond's basic proportions and the precision of its facets. Every angle and facet affects the amount of light returned or lost.
The cut-grading system developed and used by GIA applies to standard round brilliant diamonds in all clarities across the D-to-Z color range. It assigns one of five cut grades: Excellent (Ex), Very Good (VG), Good (G), Fair (F), and Poor (P).
In the GIA system, the cut grade is determined by the diamond's proportions or finish. If one proportion factor is more extreme than the others, it can lower the cut grade of an otherwise well-cut diamond. An extremely large table facet, a very steep crown angle, a very deep pavilion, or a thick girdle can reduce a diamond's cut grade significantly.
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Clarity is a gemstone's relative freedom from clarity characteristics, which are classified as inclusions and blemishes. Inclusions are enclosed within a diamond, or they extend into the diamond from its surface. Blemishes are confined to the diamond's surface. Inclusions typically have more influence on a diamond's clarity grade than blemishes.
The GIA clarity grading scale provides a universally understood method of describing a diamond. It consists of 11 grades. The following descriptions apply mostly to round brilliants in typical jewelry sizes. Characteristics might be more visibile in large stones and some fancy cuts.
Flawless
Flawless diamonds show no inclusions or blemishes of any kind when examined under 10X magnification by a skilled grader.
Internally Flawless (IF)
An IF diamond shows only insignificant blemishes and no inclusions when examined by a skilled grader under 10X magnification. Normally, the blemishes on an IF diamond can be removed by very minor repolishing. Surface graining is an exception because it usually can't be polished away.
Very Very Slightly Included (VVS1 and VVS2)
VVS diamonds contain minute inclusions that range from extremely difficult (VVSj) to very difficult (VVS2) for a skilled grader to see under 10X magnification. The inclusions in a VVSj diamond are extremely difficult to see in the face-up position, or they might be visible only through the pavilion. In VVS2, they're very difficult to see.
Very Slightly Included (VS1 and VS2)
VS stones contain minor inclusions that range from difficult (VS1) to somewhat easy (VS2) for a trained grader to see under 10X magnification. Typical includsions are small crystals, feathers, or distinct clouds.
Slightly Included (SI1 and SI2)
SI stones contain noticeable inclusions that are easy (SI1) or very easy (SI2) for a trained grader to see under 10X. Typical inclusions are crystals, clouds and feathers.
Included (I1, I2 and I3)
Diamonds in the I range contain inclusions that are obvious to a trained grader under 10X magnification. The inclusions are usually quite visible to the unaided eye and may even affect the stone's durability.
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Diamonds that range from colorless to light yellow and light brown fall within the normal color range. It's also called the D-to-Z range because of the letters assigned to the GIA color-grading scale. The GIA Color Scale begins with D (colorless) and continues through the alphabet to Z (light yellow). Within the D-to-Z range, when all other value factors are equal, colorless diamonds are the most valuable.
A diamond's color grade is based on how noticeable the color is, also known as depth of color. Because each letter in the D-to-Z scale represents a narrow color range, not a specific point, two diamonds with the same color grade can actually differ slightly in their depth of color.
The difference between one color grade and another on the GIA D-to-Z scale can have a big impact on price. The biggest jump is between the D and E grades. A 1.00-ct. D-Flawless diamond can cost a lot more than an E-color diamond of the same size and clarity. Farther down the color scale, there's still enough of a value difference to make it important to grade color carefully and under consistent conditions.
The levels of the GIA Color Scale can be divided into colorless, near-colorless, faint yellow, very light yellow, and light yellow ranges.
The D-E-F grades are considered colorless. D and E diamonds have virtually no color, and an F has a nearly undetectable amount of color that shows only in the face-down position. The differences between these grades are actually very slight. In fact, they're almost indistinguishable in diamonds smaller than 0.25 ct. Diamonds in this color range are extremely rare and valuable.
The G-H-I-J grades are near-colorless. Diamonds with these grades look colorless face-up and nearly colorless face-down. They have slight traces of color that aren't noticeable to untrained eyes when the stones are mounted. These diamonds are popular because they combine fairly high color with somewhat lower prices.
The K-L-M grades are faint yellow. Diamonds in this range show very faint yellow color face-up and face-down. When they're mounted, small stones look colorless, but large ones show a slight yellow tint.
N through R diamonds are considered very light yellow. They appear very light yellow face-up and face-down, even when they're mounted in jewelry.
S through Z diamonds are light yellow. They show substantial color face-up or face-down, loose or mounted.
Once a diamond goes beyond the Z color range, it moves into the fancy-color range, starting with Fancy Light yellow. This causes a rise in value. Sometimes, diamond rough with color in the X to Z range can be cut to achieve a fancy-color designation. |
The weights of diamonds and most other gems are expressed in metric carats. One metric carat equals 0.200 grams (200 milligrams or 1/5 gram). A carat is divided into 100 equal units called points. According to US Federal Trade Commission rulings, all weight representations are subject to a 1/200 carat (one-half point) tolerance. If other factors are equal, the more a stone weighs, the more valuable it will be.
It's diamond industry practice to weigh diamonds to a thousandth of a carat, then round the weight to a hundredth of a carat. You round the weight up only if the number in the thousandths place is 5 or more. For example, you'd round a diamond that weighs 1.764 cts. to 1.76, but one that weighs 1.765 cts. to 1.77. |
- Introduction
- Cut
- Clarity
- Color
- Carat Weight
Certain factors affect the value of any gemstone in any given state of the market, compared to others of its kind. These factors have not always been recognized or systematically evaluated. But they have always had a big bearing on value. They probably always will.
There are four value factors: carat weight, color, clarity, and cut. In the diamond trade, these are called the Four Cs. They also apply to colored gemstones, but in different ways.
The GIA Colored Stone Grading System provides standards for the industry by giving an organized way of judging color, clarity, and cut. This system is the most comprehensive of its kind. It allows evaluation and comment on any feature that affects the beauty and value of natural, transparent, faceted gems that are unenhanced (or enhanced with a stable treatment). It can be used, however, to describe any gem material, including imitations and synthetics. It can also be adapted to evaluate translucent and opaque gems, as well as cabochons, carvings, engravings, and phenomenal gems.
Colored stone shapes (seen face-up) are either the familiar round, or fancy. Some fancy shapes are basically rectangular or squarish, like the emerald cut. Others, like marquises, have various curves. Most colored stones (and larger diamonds) are cut as fancy shapes.
Because cut so greatly affects a stone's beauty, value, and durability, an important part of grading colored stones is judging how cut affects appearance, finished weight, and value.
With faceted stones, cut grading is divided into proportions and finish.
Proportion grading means analyzing the size and angle relationships between the various facets and parts of the stone, along with its overall symmetry and brilliance.
Here the grader considers the appeal and practicality of the dimensions. This includes judging the stone's length-to-width ratio, table size, girdle thickness, total depth percentage, crown height/pavilion depth relationship (important in light return), bulge (crown or pavilion) in step cuts, and balance (symmetry). It also includes looking at ease of mounting, and the presence of extra weight that adds no beauty. Finally, the grader looks for a pleasing display of color and brilliance - th emost important element of a gem's visual appeal.
Finish grading is an analysis of cutting details and the gem's surface condition. Here the grader considers the quality of the polish and symmetry, which includes the shape, positioning, and arrangement of the facets. Also considered is the appropriateness of the number of facts on the stone (for its size). A finish grade is assigned where 1 represents obvious details to 10 which represents minute details.
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Clarity means the relative degree of freedom from features called clarity characteristics. These are either blemishes on the surface of a stone or includsions inside the stone. Scratches, abrasions, and nicks are common blemishes. Included crystals or needles are examples of inclusions.
Inclusions are not necessarily bad. Many serve as internal "birthmarks" that can help identify a stone. A few materials, like amber, can be more valuable with inclusions. Many phenomenal gems, like stars and cafs-eyes, depend on the presence of inclusions, oriented in specific ways, for their optical effects. Some inclusions, like the byssolite-fiber "horsetails" in demantoid garnets, tell us a gem's identity. Others even indicate the gem's source. Finally, inclusions are important in separating some natural from synthetic material, or in giving evidence of enhancement.
Expectations of clarity, and its effect on value, depend on the kind of stone. Fine clarity in an emerald would be mediocre clarity in an aquamarine. For opaque stones like lapis lazuli, clarity has no meaning (unless we redefine it as, say, freedom from characterisitcs such as cracks and scratches).
For this reason, the GIA colored stone clarity grading system divides transparent colored stones into three clarity types. Type I stones are usually clean, like aquamarines. At the other extreme, Type III stones, like emeralds, are almost always included. Most stones fall in Type II-usually included. Thus, the clarity standards for Type I are the most exacting, II less so, and III the least.
Each clarity type is divided into seven grades ranging from VVS (Very Very Slightly Included) down to /3 (Imperfect), plus the Del (Declasse) category. Depending on the clarity type, a VVS stone may have inclusions ranging from difficult to easy to see under lOx magnification. Declasse (meaning outside the classification system) stones are so included they are no longer transparent. (But they still have a place in the market-usually as beads, carvings, or cabochons.)
Intermediate grades (from high to low) are VS (Very Slightly Included), SI (Slightly Included), and I (Imperfect). These generally represent an increasing number or visibility of inclusions. To allow for finer distinctions in the grade range where most gems fall, SI is subdivided into SIl and Sl2, and I into II, 12, and 13.
There is neither a Flawless (Fl) nor an Internally Flawless (IF) grade, as there is in diamond grading. This is because the diamond equivalent of flawless is almost impossible to find in a colored stone. In colored stones there are almost always at least surface characteristics. |
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With diamonds, usually the absence of color enhances value. But color is the most important of the Four C's for colored gems, because it basically sells a colored stone.
Often we specify gem varieties by color. These labels express the bodycolor - what you see as the stone's basic, underlying color.
Bodycolor is usually the most significant color effect. It depends on how the stone absorbs light. So judging a stone's color normally means looking for its bodycolor and ignoring other color effects such as surface reflections and multi-colored flashes.
The GIA colored stone color grading system provides a coherent, consistent color description vocabulary for communicating about colored stones.
Color grading involves two steps. First the grader describes the gem's color in terms of hue (the impression of color we notice immediately), tone (a color's lightness or darkness), and saturation (the strength or purity of a color's hue). This is done by eye, with the GIA Hue Chart, Tone Scale, and word terms from the Saturation Scale. Then the grader confirms the color match with a reference standard.
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Carat weight is the most clear-cut value factor. In the normal size range for colored stones used in jewelry, per-carat price usually increases with size. With gems like ruby that are rare in large sizes, per-carat price in larger stones rises quite dramatically.
But some gems, like blue topaz, are usually available in large sizes. So there is often little difference in the per-carat prices of medium to large stones.
In materials like aquamarine where light tones mean depth of color is a problem, very small stones may cost more per carat.
A stone that is too large will be difficult to mount and less attractive in jewelry. So oversized stones with good color are usually lower in per-carat price than the largest jewelry-sized stones. This depends more on dimensions than on weight, since different materials have different specific gravities. Usually, 20 millimeters in any dimension is the maximum for jewelry use.
Faceted gems are weighed in metric carats. One carat (ct) equals 0.2 gram. This is a little more than 0.007 (seven thousandths) ounce avoirdupois. There are almost 142 carats in one ounce avoirdupois. |
- Color
- Luster
- Spotting
- Shape
- Size
The color we see in a pearl can be a combination of three distinct characteristics: bodycolor, overtone, and occasionally orient.
Bodycolor is the pearl's basic color. Some freshwater pearls display more than one bodycolor. Pearl colors you are likely to encounter include light pinks, whites, and yellowish or brownish whites (called creams). Black includes pearls that are truly black, as well as very dark gray, very dark blue, purple, and brown. Other pearl colors include light shades of blue, silver-gray, violet, purple, orange, and yellow. Some occur more often in freshwater pearls, which tend to be more vividly colored than saltwater pearls.
There are several current theories on the causes of color in pearls. These include variations in the fineness of nacre grain, variations in pigmentation, the relative proportions of calcite and aragonite in the makeup of the nacre, proximity to certain internal organs during growth, and the nature or type of host mollusk they grow in.
Overtone refers to the one or more colors that may overlie the body-color. To understand overtone, think of a white plastic Ping-Pong ball coated with several layers of lightly tinted acrylic. If you look through the acrylic perpendicular to the surface, it looks basically white (especially the part nearest you). But toward the sides of the ball, where you look through more acrylic, you see more of the coating's color.
Many pearls have no overtone. Some have overtone only in small areas. Some have more than one overtone. Few have overtone that covers them entirely. Rose (ROE-zay-a trade term that designates a rose-colored overtone as distinct from pink bodycolor), blue, and green overtones are most common. Most overtone colors enhance some bodycolors but detract from others. Thus, they help or harm a pearl's appearance and value. A strong green overtone, for example, enhances black pearls. But it detracts from light-colored pearls.
Pearls of any color can be striking. But because different colors look best against different skin tones, and because some cultures prize certain colors more highly than others, some command higher prices. The differences vary from country to country. But high-quality pink roses, white roses, and blacks with metallic green overtone usually fetch the highest prices in the US. Cream roses are a little lower, and colored pearls lower still.
Orient is an iridescence or rainbow-like sheen that seems to hover about the surface of some pearls. It is one of the rarest, most prized characteristics a pearl can have. If present, it always enhances the quality, beauty, and value of a pearl. It is caused by white light breaking up into its component colors as it passes through nacre. Orient is rarest in spherical pearls. It is more common in baroque pearls, because their surface irregularities create more light "breakage." Strong orient is much more common in freshwater cultured pearls than in saltwater cultured pearls. This also may result from surface irregularity.
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Luster is the quality of the light reflections from the surface of a pearl. Pearls are said to have high or very high luster when the reflections are bright and sharp. They are said to be dull when the reflections are weak and fuzzy (or diffused). The best freshwater pearls have luster that equals that of the best saltwater varieties.
Luster depends on the fineness and transparency of the nacre. Fineness depends on the relative size, evenness of size, and arrangement of the calcite and aragonite platelets in the nacre. If the platelets are very small, uniform, and well-fitted, the grain, or texture, is fine. If the crystals are larger, of different sizes, or jumbled, the grain will be coarse.
Japanese cultured pearls are grown in relatively cold waters. The lower temperatures slow the rate of nacre accumulation, thus producing more and smaller crystals. As a result, Japanese cultured pearls usually have fine-grained, transparent nacre. Japanese saltwater cultured pearls (and others grown in similar environments) are usually the most lustrous of all pearls.
South Seas cultured pearls (from the Indian and South Pacific Oceans) are grown in warmer waters, which produce coarser, less transparent nacre. These and other warm-water cultured pearls are rarely as lustrous as pearls from Japan. But they generally have thicker nacre coatings.
Graders classify luster as very high, high, medium, low, and very low, and then select a numerical grade from the range the term represents. If all other factors are equal, the higher the luster, the more valuable the pearl.
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Spotting refers to the extent and severity of surface features such as bumps, dark spots, or cracks (generally called blemishes or surface characteristics). Few pearls are completely free of blemishes. There is no consensus about which type of blemish is worst. But those that seriously affect a pearl's beauty and durability seriously affect its value, too. Here are the most common blemishes.
- Bumps and Welts-Irregular protrusions too small to affect basic shape.
- Chips-Holes in the surface.
- Crac/cs-Breaks in the nacre surface or nucleus.
- Dark Spots-Dark concentrations of conchiolin under the nacre.
- Dull Spots-Areas of nacre that are markedly lighter or duller than the surrounding nacre.
- Flats-Flat sections too small to affect a pearl's basic shape.*
- Gaps-Areas where the nacre has not entirely covered the nucleus.
- Pinpoints and Dimples-Circular indentations or depressions. Pinpoints are smaller than dimples and are likely to be found in groups or series.
- Shaving or Grinding Mflrfo-Abrasions resembling small groups of scratches.
The surface irregularities of mantle tissue nucleated freshwaters hide many of the blemishes seen in saltwater cultured pearls. You can generally disregard bumps, welts, flats, pinpoints, and dimples. Dark spots and dull spots are usually the most detracting blemishes.
Spotting is graded by considering the sizes, number, locations, visibility, and types of blemishes. The spotting is classified and assigned a numerical grade from the range given: flawless, lightly spotted, spotted, and heavily spotted.
*Note: When a pearl's surface is completely covered with shallow concave depressions, it may resemble hammered soft metal. Called a hammered or martelled (MAR-tulled) appearance, this is not considered a blemish for three reasons. First, it contributes to orient. Second, its appearance resembles that of some natural pearls. Third, it usually indicates thick nacre. |
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Pearls are generally round, symmetrical, or baroque.
Round pearls are more or less spherical. The rounder a pearl is, the higher its value may be. Off-rounds are slightly distorted. Semi-baroques, while clearly distorted, do not qualify as baroque. We usually judge strands of pearls according to how closely they approach perfect roundness.
Symmetrical pearls are evenly shortened, elongated, or otherwise distorted. But they can still be visually divided into two equal and more or less identical halves. Common shapes include pears, drops, eggs, and buttons. Properly matched and strung, they make attractive necklaces. One-of-a-kind symmetricals are used in rings and pendants.
Baroque shapes are so distorted or irregular they cannot be classified as round or symmetrical. Most freshwater cultured and natural pearls are baroque. Semi-baroques fall between symmetricals and baroques. Most of the names given baroque shapes come from fancied resemblances to familiar objects-dog tooth, feather, or wing pearls. Most baroque shapes make better pendants or rings than necklaces. Because of the material used as nuclei, baroque shapes are common in freshwater cultured pearls. Rice (resembling puffed rice cereal) is the most common shape for freshwater pearls used in necklaces.
To grade shape, the grader looks closely at the roundness of all pearls on the strand, then mentally averages it. Shapes are assigned a numerical grade from the range given: all round, mostly round, slightly off-round, off-round, semi-baroque and baroque.
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As with other gems, size does not affect a pearl's grade. But it does affect price, because it relates to rarity. Large cultured pearls are rare (though not nearly as rare as comparable natural pearls); how rare depends on what kind you are dealing with.
The size of saltwater cultured pearls is usually expressed in terms of diameter measured in millimeters (one millimeter equals about 0.04 inch).
Spherical Japanese cultured saltwater pearls seldom exceed 10 millimeters in diameter. Most are between 3 and 8 millimeters. South Seas cultured pearls grow to 18 millimeters, although 5 to 14 mm is the normal range. Some freshwater cultured pearls with bead nuclei grow to 14 millimeters; most are much smaller. Rice-shaped freshwater cultured pearls typically measure about 3 to 5 millimeters. Normally, freshwater pearls, especially cultured ones, tend to be smaller than saltwater pearls, although some freshwaters are quite long.
The size of natural pearls is expressed in pearl grains. One pearl grain equals 0.25 carat. (This is 0.05 grams or a little less than 0.002 ounces avoirdupois. It takes about 565 pearl grains to equal one ounce.)
Cultured pearl dealers use the term momme (MOE-may) to express the weights of large lots of pearls. One momme equals 75 pearl grains (which makes it 3.75 grams, about 0.13 ounce, or 18.75 carats). Freshwater pearls nucleated without a bead (about 95 percent of the total freshwater production) are sold by the momme.
You may also see or hear the term once (AHNSS). It is the weight of a natural pearl squared (multiplied by itself) and used in a complicated formula to calculate value.
With natural pearls, size depends mainly on how long a pearl grows inside the mollusk. In most cultured saltwater pearls, the primary factor is the size of the nucleus. The bigger the nucleus, the bigger the pearl.
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- Introduction
- Gold
- Silver
- Platinum
A gem may be the heart of a piece, but many customers consider the artistry of the setting as important as the jewel. In fact, unless the gem is relatively expensive, the setting may account for most of the value. Also, jewelers sell a lot of jewelry that includes no gems at all-for example, wedding bands, chains, bracelets, earrings, and charms.
Obviously, then, metal is a key element in jewelry.
In chemistry, the term noble means a metal that resists oxidation or corrosion. ("Lesser" metals such as copper and iron rust and corrode easily.) So gold, silver, and the platinum family of metals are "noble" in this specific sense.
For several other reasons, this triad of metals deserves to be called "noble" in a broader sense, too. They are strong yet malleable (that is, they can be worked without powdering or shattering). They are ductile, which means they can be drawn out into thin wire. They are beautiful, with a nice weight, heft, and feel. They carry high value in easily portable weights. In short, gold, silver, and platinum are ideal for jewelry.
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Gold has the longest history of use in jewelry. Pure gold resists corrosion and oxidation, and lasts almost indefinitely. It is the most ductile and malleable metal. An ounce can be drawn into miles of wire or beaten into a sheet much thinner than paper.
Although gold is found everywhere on our planet-from its seas to its creeks and rivers, from its interior to its crust-it is scarce. All the gold ever found totals only around 100,000 tons.
We mine gold primarily from two kinds of deposits: veins and placer (PLASS-er).
Veins occur when molten gold and other minerals are flushed up as hot liquids from the Earth's interior. When they hit cooler rocks near the surface, they crystallize. The crystalline mix of gold and other materials fills cracks and fractures, leaving veins of ore in the rock. These are called primary deposits.
Erosion of gold veins by wind and water creates placer deposits. The gold nuggets, flakes, and powder (dust) ending up near the original deposit are called eluvial deposits. But the fragments initially washed into gullies, creeks, and rivers, and then finally settling into the gravel or sand due to an interruption in the flow of the water create alluvial deposits.
Pure gold is expensive and soft To reduce cost and make a more wearable product, metalworkers alloy it with other metals. (This also changes its color.) The different metals are melted together, mixed thoroughly, and allowed to solidify.
Jewelers deal with various gold alloys, collectively called karat gold. Karat (K) tells the number of parts, by weight, of gold in 24 parts of alloy. Fine (pure) gold is 24K An alloy that is 18 parts fine gold and 6 parts other metal is 18K. If it is 12 parts fine gold and 12 parts other metal, it is 12K.
The gold content of an alloy is indicated by a karat stamping. This is the common measure of gold purity in the US. The highest karat gold normally used in Western countries is 18K. The lowest is normally 10K (9K in England). In the US, this minimum karatage, the lowest that can legally be called gold, is commonly used for class rings and the popular, lower priced lines of rings that feature initials, synthetic birthstones, and inexpensive colored stones. The gold mountings used for diamond jewelry are generally 14K or 18K.
While American manufacturers use the K numbers in their quality stampings, foreign manufacturers often stamp their products with a three-digit number that gives the gold content as parts per thousand. So 750 inside, say, an Italian-made ring indicates 18 karat gold; a stamping of 585 corresponds to 14 karat gold.
Federal Trade Commission (FTC) guidelines clearly state that karat level must be specified in describing jewelry. Unless the piece is 24K, do not use the terms gold or solid gold alone. (You can use either term on items made throughout of 10K or higher gold alloy, however, if the karat fineness is shown just as clearly right before it. For example, you could not advertise a 14K gold ring only as a gold ring or a solid gold ring. You could, however, advertise it as a 14K gold ora!4K solid gold ring.)
Since 1976, a new US gold labeling act requires karat gold items sold interstate, or imported into or exported out of the US, to meet tolerances dictated by the plumb gold standard. Plumb gold is karat gold whose pure gold content is within three parts per thousand of the stamped K mark for unsoldered items, or seven parts for soldered items. (Previously, unsoldered karat gold could be off by as much as 1/2 karat, soldered jewelry by a full karat.)
Fine gold (24K) or alloyed yellow gold (karat gold) around 22K has a distinctive yellow color. The lower K levels may begin with a slightly paler yellow color, but this depends on the alloy mix.
Alloying also produces colored golds, including white, red, green, and blue. Common alloys include silver, copper, nickel, and iron, alone or combined in varying proportions. Sometimes traces of one or more additional metals, such as zinc, tin, manganese, or cadmium, are added.
White gold contains no silver, and little or no palladium. Gold of 14K and lower is generally alloyed with zinc to make it more malleable.
Some people cannot wear certain types of karat gold (although most people can wear 18K or higher). A few are allergic to it or to one of the alloying metals. With others, a reaction between the alloys and the body acids on the skin, even in 14K gold, leaves a dark residue. This can also be caused by chemicals in cosmetics, or in the environment (especially smog or ocean air). Occasionally, dust particles on the skin or in clothing act as an abrasive, rubbing off minute bits of gold and leaving a smudge. |
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Silver has a long history as money, and is the longest-used white jewelry metal. It tarnishes easily (unless it is rhodium-plated), is less durable than gold, and is harder to work because it conducts heat so well. But it has a lovely look and feel, takes a high polish, and is less rare and expensive than gold and platinum. Thus, it remains a popular jewelry metal.
There are several levels of purity in silver alloys.
- Britannia silver must be at least 95.84 percent pure silver by weight.
- Mexican silver usually contains 95 percent silver and 5 percent copper. So it, too, is more pure than sterling. (Not all silver produced in Mexico is Mexican silver.)
- Sterling Silver must be at least 92.5 percent pure (the rest is usually copper). Its hardness is superior to that of pure silver. Anything containing less silver cannot be called either "silver" or "solid silver" in the United States.
- Coin silver is alloyed in the proportions once found in US silver coins. It must have 90 percent fine silver to 10 percent copper, according to FTC guidelines. It cannot be legally called sterling. (The European market handles alloys with 87.5,83, and 80 percent silver. Bach should be marked with its actual fineness)
Like gold, silver is used in forms other than solid alloys.
- Silver filled refers to mechanical plating with a silver alloy of at least 92.5 percent fineness. The plating must make up at least 1/20 of the weight of metal in the article. It can also be called silver overlay, but never silverplate.
- Silverplate is a fine silver film deposited on a base metal by electrolysis, in the same kind of electrically charged bath used to make gold electroplate. Chains and beads are often coated or electroplated in this way. A sil-verplated item cannot be called sterling or bear a hallmark saying "silver."
- Vermeil (vur-MAY) is sterling silver with a gold overlay or plating.
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Platinum, the newest (and some feel, the preeminent) fine jewelry metal, was thought to be an "unripe" form of silver by Spanish explorers who found it in South America. It was identified as a new metal in the 1700s.
Platinum is more rare and expensive than gold. It offers fine stone-holding power and durability. Its non-tarnishing, grayish-white color is ideal for setting colorless and near-colorless diamonds. The heyday of platinum jewelry was in the 1920s and '30s. But recent years have seen a renaissance in it, particularly in Japan.
Platinum occurs in association with other rare metallic elements collectively called platinum group metals. They include platinum, iridium, palladium, ruthenium, rhodium, and osmium. Platinum is the most abundant. But all (except osmium) are used in jewelry, usually in alloys (especially 90 percent platinum/10 percent iridium hardener). Rhodium plating adds durability and brightness to platinum, white gold, and silver, and slows tarnishing on sterling silver. It is also common to rhodium-plate yellow gold heads in which diamonds are set.
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