Diamond Guide

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Diamond Grading: The 4 C’s

The 4 C’s, when referring to diamond value, are color, clarity, carat weight and cut. All four factors are equally important in determining the final cost of a diamond. The criteria for diamond grading, most respected internationally, was developed by the Gemological Institute of America (the G.I.A.). The terminology and systems described on this page, are those of the G.I.A.

Following, is an explanation of these terms.

Color

The color of a diamond refers to the relative amount of yellow, brown or gray body color that a stone possesses. The G.I.A. scale starts at “D” and goes through “Z”, with “D” being void of any body color, and “Z” having a light yellow, brown or gray color.

With actual stones, the color difference would appear like this:

Clarity

Practically all diamonds contain naturally occurring internal characteristics called inclusions. The size, nature, location and amount of inclusions determine a stone’s clarity grade and affect its cost. Clarity is determined using 10X magnification. By definition, if something is not visible at 10X, it does not effect the clarity.

Flawless VVS1 VVS2 VS1 VS2 SI1 SI2 I1 I2 I3
Flawless/Internally Flawless= No inclusions visible, by an expert at 10X magnification
VVS1-VVS2= Very, Very slight inclusions very difficult for an expert to find under 10X
VS1-VS2= Very slight inclusions difficult for an expert to find under 10X
SI1-SI2= Noticeable, relatively easy to find under 10X. Not visible w/o magnification in a face-up direction.
I1-I3= Obvious under 10X, may be visible to the unaided eye, I3′s inclusions may effect the stone’s durability.

Carat Weight

Carat is a unit of weight, not size. There are 5 carats in a gram. The weight of a diamond is measured in carats. A carat is divided into 100 parts, called points.

1   carat =1.00 carat=100points
1/2 carat= 0.50 carat= 50 points
1/4 carat=0.25 carat= 25 points

Cut

At the turn of the last century, it was mathematically determined, what the optimal proportions for a diamond should be to assure maximum brilliance and dispersion. Those proportions are as follows:

quality of a diamond’s cut makes all the difference in how the stone appears. A poorly cut “D”, Flawless stone, can look dead and lifeless, whereas an ideally proportioned diamond of much lower color and clarity will appear radiant and dazzling. So, why aren’t all diamonds ideally proportioned? The answer is quite simple. Diamonds are sold by weight. Stones cut to ideal proportions waste more of the diamond crystal, therefore weigh less than stones that are cut to maximize weight.

Here are examples:

The diamond below will weigh more because of the shallow crown, and exaggerated table size. Not to mention, that another diamond of shallow proportions could be cut from the remaining crystal.

General Enhancement Categories:

  • Treatment Code N: Those natural stones which are not currently known to be enhanced by any methods, such as spinel, and therefore can safely be presumed to be untreated have the code N (not enhanced). The code may also be used for stones that are sometimes or often treated but in this particular case are unenhanced. To use this symbol on sapphire, for example, which is generally heated, means that the seller certifies that the particular stone was not heated and can supply a document such as an invoice or lab report so stating.
  • Treatment Code E: Those natural stones which are routinely enhanced by traditional methods have the code E (enhancement). The particular stone given this designation may or may not be enhanced. For example, since most emeralds are oiled, an E would indicate such treatment but would not cover non-traditional methods, such as hardened plastic resins (like Opticon), which would require specific enhancement codes. Another example would be the use of E for aquamarine, which in most cases is heated prior to the sale of the rough to remove greenish tints. If the seller knows what specific treatment has been used, then a more specific code should be used.
  • Other Treatment Codes: Those gemstones for which definite information on standard treatments is known or to which N and E codes do not apply due to non-traditional treatments, must disclose the specific treatment with the appropriate code. For example, a morganite that is known to have been heated would receive an H code rather than the less specific E code.

Specific Enhancement Codes:

  • Enhancement Code B: Bleaching is the use of chemicals to lighten or remove a gem’s color.
  • Enhancement Code C: Coating is the use of surface treatments, such as films or lacquers, to provide color or other special effects. NOTE: This type of treatment is not permanent and can chip or wear off. Do not use harsh solvents or chemicals on jewelry with this type of treatment. Read our care guide for more information on protecting gemstone jewelry.
  • Enhancement Code CR: This designation is used for any stone that is synthetic or laboratory created.
  • Enhancement Code D: Dyeing is the introduction of coloring matter into a gem to give it a new color or greater intensity.
  • Enhancement Code F: Filling is the incorporation of colorless borax or other substances into the cracks that are a by-product of heating the stone; it is used only if a crack is visible at 10x magnification.
  • Enhancement Code G: This code refers to the use of gamma or electron irradiation for the purpose of changing a gem’s color. Irradiation may be followed by a heating process to stabilize the color. Such stones do not exhibit residual radioactivity.
  • Enhancement Code H: Heating a gem at a high temperature improves clarity, changes color or creates phenomena in gems. Any filler materials that enter the gem as a result of the heat treatment must not be visible in fractures at 10x magnification.
  • Enhancement Code L: Jewelers sometimes use a laser to drill into a stone and remove or alter an inclusion, specifically on diamonds. Lasering is the name of the treatment.
  • Enhancement Code O: Oiling, or resin infusion, is the intentional filling of surface breaking cavities and cracks in transparent or translucent gems with a colorless oil, wax, resin or man-made unhardened resin.
  • Enhancement Code R: Irradiation is the use of neutron bombardment to alter color. This process creates residual radioactivity, and such stones must receive a Nuclear Regulatory Commission safety release prior to sale. The irradiation treatment often is used in combination with other radiation and heating treatments.
  • Enhancement Code S: Bonding is the intentional use of a colorless agent (usually plastic) within a porous gemstone.
  • Enhancement Code TA: Type A jade is natural jade enhanced only with wax.
  • Enhancement Code TB: Type B jade is natural jade that is bleached in acid to remove undesirable staining, and then impregnated with wax or polymers.
  • Enhancement Code TC: Type C jade is natural jade that is dyed and sometimes bleached and impregnated with wax or polymers.
  • Enhancement Code DS: The diffusion treatment uses coloring and star-making chemicals to affect a gem’s appearance. It adds specific chemicals to a high-temperature heating process to penetrate the surface layer (usually to a slight depth only). Such treatment is not generally accepted, and stones sold with this enhancement must be specifically labeled as diffused.
  • Enhancement Code W: Waxing/oiling is the impregnation of colorless wax, oil or paraffin into porous opaque gems to improve appearance.
  • Enhancement Code DBL – Doublet: Jewelers make a doublet by gluing a thin layer of natural stone to a backing material. The backing material is used to thicken and give strength to the item.
  • Enhancement Code TPL – Triplet: A triplet is a doublet that has a clear protective layer on top of the stone. The top layer may consist of clear quartz, glass or hard plastic. This layer thickens and gives additional strength to the item.