Gemstones are evaluated using the same 4Cs we discussed in our diamond guide. These 4Cs are color, cut, clarity, and carat weight (size).
Gemstones are compared to other stones of the same type. The rarity of a gemstone affects the value. Treatments can either increase or decrease the value compared to a gem that is natural and untreated.
Inclusions can also either increase or decrease gemstone value. For example, a star sapphire is more valuable because of the inclusions. They can also indicate locality (where that gem was mined).
Values are affected by provenance, where the stone came from and history. Finally, the demand for a particular gemstone increases the price.
If you are not sure what kind of gemstone you have, start with the color. The most common are in bold text.
If you aren’t sure what kind of gemstone you have, we can determine that for you.
Gemstones come in all shapes and sizes. The most common are:
Gemstones are cut in the most flattering shape for each type of gem. The shapes above can be faceted to create complex shapes such as checkerboards or cabochons.
As mentioned previously, enhancements can increase or decrease the value of a gemstone. The FTC requires sellers to clearly disclose key specifics about gemstones:
“With the exception of the normal fashioning (cutting and polishing) of a gemstone, it is the seller’ s responsibility at all levels of commerce to clearly disclose to the buyer at the time of sale:
The American Gem Trade Association (AGTA) advises if a treatment is not known, but suspected because such stones are commonly treated, the FTC states that “it is prudent and appropriate to disclose gemstone treatments” that may apply.
Many gemstones are treated to bring out attractive qualities or make them more durable. The following are the gemstone enhancement codes:
N = Not Enhanced: Natural stones which are not commonly enhanced. If a gemstone is commonly enhanced, the seller must provide a guarantee it is natural to use the “N” symbol.
E = Enhanced: Traditional enhancements for that gemstone.
ASBL = Assembled from multiple stones.
B = Bleaching: chemically treated to bleach or remove color.
C = Coating: coatings or films to improve appearance.
D = Dyeing: colored dye to improve or change the color.
F = Filling: flux or similar clear filling to improve appearance, increase durability, or add weight.
H = Heating: heat used to increase phenomena or alter color or clarity.
HP = Heat and Pressure used to increase phenomena or alter color or clarity.
I = Impregnation: surface impregnated with a filling to add weight or improve appearance or durability.
L = Lasering: a laser or chemicals used to enhance the clarity of inclusions inside, typically on diamonds.
O = Oiling/Resin: improving the appearance by filling surface fissures with a colorless substance such as resin, oil, or wax, but not plastic or glass.
R = Irradiation to enhance the color or reduce the visibility of inclusions.
U = Diffusion: the use of high heat and chemicals to induce a thin layer of color or asterism (as in star rubies).
W = Waxing/Oiling improves the appearance of opaque stones by infusing a colorless oil, wax, or parrafin.
SC = Special Care to prevent loss of enhancements: usually by avoiding light, chemicals, heat, and ultrasonic cleaners.
CMP = Composite stones are created using more than just a gemstone, often lead glass or polymers.
* These codes and treatment types must be used as directed in the Gemstone Information Manual.
The American Gem Trade Association provides codes which are fully explained starting on page six of the Gemstone Information Chart.
Diamonds that are the most clear and lacking in color are the most valuable. Colors are graded on a scale from D to Z described as:
These differences are not visible to the naked eye. Diamonds are graded by comparing them to masterstones (brilliant diamonds of known color) under controlled conditions.
Each diamond shape is cut in a different manner to enhance the sparkle and brilliance. Diamonds come in ten common shapes plus more exotic shapes including:
Cut is evaluated by being the ideal depth for the stone. Shallow cut diamonds lose brilliance because they lose light from the bottom. Deep cut diamonds appear dull and less bright because they lose light from the sides.
Round diamonds are the most common and GIA provides a five point cut scale from poor to excellent to value a diamond’s cut.
Appearance is valued based on:
The remaining four components of the round diamond’s assessment are weight ratio, symmetry, polish and durability.
Diamonds are judged by the number of flaws they contain. Flawless diamonds are extremely rare, so most diamonds will have some flaws.
Surface flaws are known as blemishes while flaws within the stone are called inclusions. The degrees of flawlessness are defined as:
Most diamonds grade as VS or SI. The fewer flaws, the more valuable the diamond.
Diamonds are weighed in very precise measurements to the hundredth decimal points. Each “carat” is 200 milligrams or .2 grams or .007 of an ounce.
A carat can be divided into 100 points to express fractions of a carat. So a half-carat diamond could also be referred to as a
“50 pointer”.
While larger diamonds are more valuable than smaller diamonds of the same quality, the value of a diamond is based on all of the 4Cs, not simply the weight.
Gold is the ideal metal for strength and durability. Because pure gold is very soft, alloys of gold, silver, copper, nickel, zinc and palladium are used.
The karat indicates the percentage of gold with a higher number indicating more gold. There are 24 karats (24k) in 100% gold. 24k gold is too soft for making jewelry for frequent wear.
18k gold is 18 parts or 18/24 gold. 14K is 14/24 gold. The balance is an alloy of one or more other metals.
White Gold is a mixture of pure gold and other metals, often nickel. Palladium is commonly used in white gold in Europe and for hypoallergenic jewelry. Some white gold my include zinc, tin, or less commonly silver.
Rose Gold is created from an alloy of gold, copper, and silver. Varying the percentages of each metal changes the hue from lighter to pink or more red.
Green Gold can occur in nature when gold and silver deposits combine into a metal known as electrum. It still needs to be alloyed with zinc or nickel for strength.
Gold Plated, Gold Filled, Gold Overlay, Rolled gold plate (RGP) all refer to a layer of at least 10k gold over a base metal, usually nickel. 12k and 14k are also used for gold plating.
According to the FTC, gold plated items should be marked to indicate the karat quality of the gold and the type of plating. For example, “14k RGP” or “12k gold overlay”.
If the metal is more than 1/20 of the weight of the entire piece, the fraction should be marked on the item. For example, “1/40 10k gold filled”.
Gold Electroplate uses an electrolytic process to layer at least .175 microns thick of at least 10 karat gold onto a base metal.
Vermeil is sterling silver plated or coated with gold.
Rhodium plating, rodium dip, or rodium flashing is frequently used on silver, white gold, and palladium jewelry. It is resistant to scratches and tarnishing and adds a luster.
Sterling Silver is an alloy of 92.5% pure silver and copper. Look for the markings Sterling, S925, 925, or ss on jewelry to indicate sterling silver. If you do not find one of these markings, the jewelry is probably silver plate.
Eco Silver is recycled sterling silver.
The Ice Test: Silver melts ice much faster than silver plate or other metals. So if a piece melts ice as fast as known silver or faster than known silver plate, it is most likely silver rather than silver plate.
Silver Plate is a thin layer of silver over another base metal, typically copper, brass, or nickel. Silver plate items are usually marked EP, EPNS, Silver on Copper, or have no mark.
Test: If the metal is flaking or a magnet sticks to your silver item, it is silver plate not silver.
Silver with a lower silver content than Sterling Silver is marked 900 or 800. Quality silver from Europe will have hallmarks indicating the maker, purity, and country (assay office mark). These hallmarks can be used to narrow down the age of antique silver. Some newer silver is marked with
date letters.
Argentium Silver is 93.5% recycled silver and 6.5% germanium. Unlike Sterling Silver, Argentium Silver is hypo-allergenic, tarnish resistant, more durable, and stronger than Sterling Silver. It is shinier than silver, platinum, or white gold.
Brittannia Silver has a higher silver content than Sterling Silver. It is marked 958 which is exactly 958.4 or 95.8% pure silver. It is not commonly used in modern jewelry, but may be found in antique pieces.
Palladium is more rare than Platinum and twice as strong as gold. For jewelry, 95% pure Palladium is alloyed with 5% silver, copper, nickel, chromium, or manganese.
It is highly tarnish resistant and a good choice for jewelry. However, it is considerably more expensive than Platinum.
Identification marks on Palladium are 999 (99.9% pure), 950 (95% pure) 500 (50% pure) plus a maker’s mark, and a convention mark. A five-sided pentagon shape with a curved base is the international Palladium hallmark.
Platinum is a naturally white precious metal ideal for making jewelry. It is strong and tarnish resistant. Platinum is preferred as the best metal to safely retain precious gemstones. Because jewelry is made with 95% platinum and 5% Iridium or Cobalt, it is hypoallergenic.
To identify platinum, look for the markings Platinum, PLAT, or PT and the purity indicators 950 or 999.
Cobalt Chrome is commonly used in men’s wedding bands. It the most durable bright white metal used for jewelry. And Cobalt Chrome is more affordable than white gold or platinum because it is not a precious metal.
Cobalt Chrome is a hypoallergenic alloy made of primarily cobalt and chromium. It polishes into a brilliant luster and requires no maintenance because it will not oxidize.
Stainless Steel and Blue Steel are durable, lightweight, inexpensive and last longer than most metals. But steel is it not a precious metal and has little inherent value.
Titanium is lightweight and stronger than precious metals. It is not rare so not a precious metal or valuable.
Tungsten Carbide is stronger than Titanium, tough, scratch resistant, and naturally hypoallergenic. It is often found in men’s or matching wedding bands. It is not considered a precious metal.
Zirconium, Black Zirconium, Gray Ziconium is naturally a silver-gray color. Heat is used to create a hard charcoal gray or black oxide finish. It is inexpensive and not a precious metal
