DAMASCENING
Damascening is the inlaying of a soft metal (like silver or copper) into a hard metal (like steel). The name comes from the city of Damascus, where this process was first used.

DEMANTOID GARNET
Demantoid garnets are valuable green, very lustrous garnets with a cubic crystalline structure. They are a rare variety of andradite. Demantoid garnets have characteristic inclusions that look like horsetails. Demantoid garnets have a hardness of 6-7 and a specific gravity of 3.8 - 3.9. Demantoids were very popular in the 1800's, but are rarely used today.

DEMI-PARURE
A demiparure is a matching set of jewelry, usually containing a necklace, earrings, and a pin. See parure.

DIADEM
A diadem is a tiara, a circular or semi-circular piece of jewelry worn on the head.

DIAMANT?
Diamant? is another word for rhinestone.

DIAMOND
Diamonds are precious, lustrous gemstones made of highly-compressed carbon. Diamonds are one of the hardest materials known. Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419. Colors of diamonds range from colorless, yellow, orange, brown, to almost black. Rarer colors are red, blue, green, and purple; these colors (called fancies) are quite valuable. Canary diamonds have a deep yellow color. A diamond's value is based on the "4 C's": color, cut, clarity, and carat weight. A diamond's color (saturation) is rated on an alphabetical scale ranging from D (white) to Y (yellow). "Z" diamonds are fancy, or deep-colored diamond. A diamond's cut is designed to maximize the stone's natural "fire"; brilliant cuts are preferred. A diamond's clarity depends on the number and size of its flaws and inclusions (of other minerals, like quartz). Clarity is rated from FI (flawless), IF (flawless at 10x magnification), a series of V ratings (very small flaws at 10x magnification), a series of S ratings (small flaws at 10x magnification), to I1, I2, and I3 (having inclusions visible to the naked eye). A diamond's carat weight is simple how much it weighs (a carat is about 0.2 grams or about 0.007 ounces). The largest-known gem-quality diamonds include the Cullinan (aka the Star of Africa, 530.20 carats), the Excelsior, the Great Mogul (an ancient Indian diamond which is said to have originally weighed 787.5 carats, but its location is not not known and nothing about it has been authenticaed), the Darya-i-Nur, the Koh-i-Nur, and the Hope diamond (named for its purchaser, Henry Thomas Hope).

DIAPERING
Diapering is a crisscross pattern of diamond-shaped lines on a raised-dot enamel pattern.

DICHROISM
Dichroism is the property of having more than one color, especially when viewed from different angles. Many minerals (like rubies and axinite) are naturally dichroic. This effect can be artificially caused by a thin layer of a metallic oxides that is deposited on the surface of a material. Dichroic coated glass transmits some wavelengths of light and reflecting others, giving it an opal-like appearance.

DIE STAMPING
Die stamping (also known as machine-stamping) is a process in which sheet metal is cut and shaped between two dies, forming a pattern in relief. Two steel dies are used, the male die has the design in cameo (protruding); the female die has the design hollowed out. The male die is put on top of the metal, the female die is put on the underside of the metal. The press is forcefully brought down onto the dies and metal, forcing the metal into the shape of the mold. Many medallions and mass-produced jewelry findings are made this way.

DIFFUSION TREATED
Diffusion treated stones are color-enhanced (not naturally colored) stones. The diffusion process only colors the outer surface of the stone, so chipping or repolishing will result in a loss of color. Diffusion-treated stones are already-cut stones that are heated in the presence of other compounds (like iron oxide, chromium oxide, titanium dioxide, etc.) that will infuse the extreme outer surface stone with color. Under a microscope, you can see the loss of color within each tiny scratch. Diffusion treatment can also change the stone's refractive index. Also, if the stone is faceted, the color will appear stonger where the facets meet.

DOG COLLAR
A dog collar (also known as "collier de chien") is a type of short, multiple-strand choker-style necklace that fits tightly against the neck. Dog collars are also known as " plaque de cou" (meaning "neck badge") when they are fastened by a clasp in the front. Dog collars are 14"-15" in length.

DOUBLET
A doublet (also dublette) is a gem made from two layers in order to save expenses; the lower part of the composite stone is glass or a non-precious stone, the top is the more valuable stone. Many different types of doublets have been manufactured (including opal doublets). One common doublet contains a layer of real garnet and a layer of glass. A thin, red garnet top is glued to a colored glass bottom. A green glass bottom with a red garnet top layer produces an emerald-like stone. A diamond is enlarged by cementing it to a crystal base.

DOUBLY REFRACTIVE STONE
In doubly-refractive stones, the light entering the stone is split into two light rays, and the rays travel in different paths. These stones have more than one refractive index. Calcite, peridot, zircon, tourmaline, and titanite are doubly-refractive stones. Birefringence is another name for double refraction.

DROP CUT
A drop cut (or briolette) is a pear-shaped cut gemstone with triangular facets on top. This type of stone makes a nice pendant.

DRUZE
Druze is a layer of crystals that form within a mineral crust, like the inner cavity of a geode. Amethyst crystals are often found in a druze. The inner cavity of agate geodes are often lined with a druze of sparkling quartz crystals.