CULLINAN DIAMONDS GLOSSARY
Below please find the diamonds glossary terms from G - L
Gemological Institute of America (GIA): Founded in 1931 by Roger Shipley, this non-profit organization upholds the highest standards for grading diamonds and other precious gems. The GIA has one of the most-respected and well-regarded gemological laboratories in the world; GIA was responsible for developing and standardizing the diamond grading system that is used today by nearly all other gem labs.
Grading Report: Sometimes called a “certificate”, although labs do not “certify” diamonds. The grading report, issued by an independent laboratory, should accurately describe the 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 Center: A small area of concentrated crystal structure distortion, usually associated with pinpoints.
Girdle: The outer edge, or outline, of the diamond's shape. 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; thin; medium; slightly thick; thick; extremely thick. While it is less desirable for a round diamond to display an extremely thin or extremely thick girdle, such girdle widths are more common and acceptable in fancy shapes.
For example, shapes such as pears, marquises or hearts may be cut with extremely thick girdles at their points (and at the cleft, in the case of a heart) in order to protect these delicates corners from damage. Most diamonds have smooth girdles that are fashioned by a "bruter" (a diamond cutter who is responsible for shaping the diamond's basic outline) early on in the cutting process. In some cases, cutters go a step further and do additional cutting on the girdle. In these cases, they may decide to create a "polished" girdle or a "faceted" girdle. In both cases, the difference between these and a regular, smooth girdle is generally not distinguishable to the eye. A polished or faceted girdle doesn't improve a diamond's grade. Most labs grade a girdle's thickness, not its appearance.
Heart - Shape Cut: A type of fancy diamond cut, which is cut to resemble the popular Valentine's Day shape. (Heart - Shape Cut - see graphic to right)
Hardness: Mineral's resistance to scratching on a smooth surface. Mohs scale of relative hardness consists of 10 minerals, each scratching all those below it in scale and being scratched by all those above it.
Hue: Pure, spectral (prismatic) color. Hues include gradations and mixtures of red, organe, yellow, green, blue, violet and purple.
IGI: International Gemological Institute. A laboratory which offers a grading report. IGI also produces written appraisals.
Included Crystal: A mineral crystal contained in a diamond. Inclusion: Imperfection internal to the Diamond.
Inclusion: A clarity characteristic found within a diamond. Most inclusions were created when the gem first formed in the earth.
Internal Graining: Internal indications of irregular crystal growth. May appear milky, like faint lines or streaks, or may be colored or reflective.
Irradiated Diamond: A diamond which has been exposed to radiation.
Knot: An included diamond crystal which reaches the surface of a polished diamond.
Laser Drilling: A diamond enhancement technique whereby a laser is used to drill to an inclusion which is then bleached to enhance the diamond’s appearance.
Laser - Drill Holes: One of the few man-made inclusions that can occur inside a diamond. Why on earth would anyone want to drill holes into a perfectly good diamond? It may seem counter-intuitive, but drilling this type of hole into a diamond can actually raise its clarity grade. In some diamonds, the clarity grade may be determined mainly by the presence of just one or two dark included crystals in a diamond that is otherwise relatively free of inclusions. In certain circumstances, the diamond cutter will decide to use a procedure to remove the dark inclusions and, hopefully, increase the clarity of the diamond. First, a hole is precisely made with state-of-the-art equipment; it extends no further than it needs to, and its width is so small (about the size of a pinpoint) that a loupe or microscope is usually required to detect it. Next, a strong acid solution is forced into the new hole.
Since diamonds are resistant to acids, the solution actually dissolves the included crystal while leaving the diamond completely unharmed. The end result is a more transparent diamond. The structural stability of the diamond is not compromised in any way by this hole, and the process is permanent.
Length To Width Ratio: A comparison of the length and width of the girdle outline on fancy-shaped diamonds. The ratio is found by dividing the length of the diamond by the width. The width is always stated as 1. Some L to W ratios are considered to be more appealing than others, but this is a matter of personal preference.
| Pear | 1.50 - 1.75 : 1 |
| Marquise | 1.75 - 2.25 : 1 |
| Heart | 0.98 - 1.02 : 1 |
| Oval | 1.33 - 1.66 : 1 |
| Emerald | 1.50 - 1.75 : 1 |
| Radiant/Princess | 0.95 - 1.05 : 1 |
Length-To-Width Ratio: A comparison of how much longer a diamond is than it is wide. It is used to analyze the outline of fancy shapes only; it is never applied to round diamonds. There's really no such thing as an 'ideal' ratio; it's simply a matter of personal aesthetic preferences. For example, while many people are told that a 2 to 1 ratio is best for a marquise, most people actually tend to prefer a ratio of around 1.80 to 1 when they actually look at marquises. And though the standard accepted range for the length-to- width ratio of a marquise generally falls between 1.70 to 1 and 2.05 to 1, there are customers who insist on having 'fatter' marquises of about 1.60 to 1 and other customers who want longer, thinner marquises of 2.25 to 1.
Loupe: A small magnifying lens used to examine diamonds. 10x magnification is the standard.
Lower - Girdle Facet: The facets on the pavilion of a round brilliant just below the girdle.
