A grade in GIA’s Color Grading System…. at the beginning of the “Near Colorless” category.
Abbreviation for Greenwich mean time. Time is calculated from the naval observatory at Greenwich, England, which is located at zero degrees longitude.
Gas Escape Valve
A one-way valve used in the Sea-Dweller, by which the helium particles are allowed to escape from the watch’s case during decompression. Sometimes called a helium escape valve.
The centimeter-gram-second electromagnetic unit of magnetic flux density, equal to one Maxwell per space centimeter. [After Karl F. Gauss (1777-1855)]. The American Heritage Dictionary, Second College Edition. Copyright 1985 by Houghton Mifflin Company. All rights reserved. Please Note: The Rolex Milgauss gets part of its name from this term (i.e. Mill-Gauss).
Gem / Gemstone
A mineral or organic material with sufficient beauty, rarity, and durability to become desirable enough to be set into items of jewelry.
Gemological Institute of America (GIA)
In 1931, Robert M. Shipley founded the Gemological Institute of America in Los Angeles. In the same year, he published his groundbreaking book, Gemology, and by that summer, 250 jewelers had enrolled in his courses. Some would later become instructors and researchers at the Institute. Since that time GIA has become the world’s foremost authority in gemology. GIA’s mission is to ensure the public trust in gems and jewelry by upholding the highest standards of integrity, academics, science, and professionalism through education, research, laboratory services, and instrument development. GIA was responsible for developing and standardizing the diamond grading system that is used today by nearly all other gem labs.
Gemologist / Graduate Gemologist
A person who studies gems…. normally a diploma is associated with this title. If there is no diploma then if a person who has a love of gems could be called a “rock hound” or an “amateur” gemologist. A person who has successfully completed recognized courses of study in gem identification, grading and pricing, as well as diamond grading and appraising is a Gemologist. There are many different institutions that can bestow the title of Gemologist…. a “Graduate Gemologist” is mostly associated with the Gemological Institute of America and a “Certified Gemologist” with the American Gem Society. I have the title of GG, so I will show my title as follows- Bud Boland, GG(GIA).
GIA-GTL, Gemological Institute of America’s Gem Trade Lab
The well-respected independent laboratory which grades diamonds and provides other services for the diamond and colored stone trade. GTL has labs in many countries around the world.
Gilt (or Gild)
Gold plated, or having a gold color or hue.
The widest point in circumference of a gem. This is the point where a gem is usually held by fingers or tweezers for examination.
The 32 triangular facets that adjoin the girdle of a Round Brilliant Cut diamond, 16 above and 16 below the girdle. Also called upper and lower girdle facets, upper and lower break facets, top and bottom half facets, skew facets or cross facets. Facets are sometimes placed directly on the girdle, in which case the stone is usually said to have a “faceted girdle”.
When the reflection of the girdle that is viewable inside of the table facet.
The measurement of the girdle and the resulting thickness percentage of the diamond’s average girdle diameter or the diamond’s width. The girdle is not graded, but rather it is described by its appearance at its thinnest and thickest points. The descriptions of girdle thickness range as follows: Extremely Thin, Very Thin, Thin, Slightly Thin, Medium, Slightly Thick, Thick, Very Thick, or Extremely Thick. The girdle should be just thick enough to protect the diamond in setting and normal wear. For a Round Brilliant Cut diamond the girdle should be from Slightly Thin to Medium to Slightly Thick… anything out of this range is the result of trying to retain weight from the diamond rough. A Fancy Shape Diamond should have thicker girdle area at the points of a Marquise Cut or Pear Shape diamond.
One of the initial steps of the fashioning process of a diamond in which the stone is given an outline shape. The stone is held in a lathe, or cutting machine, and another diamond, called a sharp, which is affixed to the end of a long dop that is supported by the hands and under an armpit, is brought to bear against the stone behind shaped. An older method consisted merely of rubbing two diamonds together until the desired outline shape was obtained.
A precious metal which has been used in jewelry for centuries. Gold will never tarnish, rust or corrode. It has also been used as a store of value to build wealth and shield against hard times. Gold used in jewelry is almost always alloyed with other metals since gold in its pure form is very soft and malleable, and would not wear well by itself.
An acceptable, lower priced diamond with adequate proportions.
Sometimes called a “certificate” or a “cert”, although labs do not “certify” diamonds. The grading report, issued by an independent laboratory, should accurately describe the measurements, proportions, weight, color, clarity, symmetry, polish and possible fluorescence seen in the diamond being evaluated. Some labs such as GIA and AGS are felt by many experts to be more consistent and stringent in their grading than some other labs.
Grain and Grainer
A trade term referring to a diamond’s weight. A grain is equivalent to 0.25 carats…. so a 4 grainer = 1.00ct., a 5 grainer = 1.25ct., etc.
A small area of concentrated crystal structure distortion, usually associated with pinpoints.
A clarity characteristic resulting from irregularities in the growth direction of a diamond crystal. Appears as faint single line or groups of lines. Much like the grain seen in a piece of wood.
One of the the technical terms used to refer to the luster of a gemstone. Jadeite is an example of a gem with a greasy luster.
French term meaning ‘engine-turned.’ This term is also used to describe the ‘honeycomb’ textured dial found on some Rolex models