The Four C's of Diamonds

Diamond Color

Most people believe that all diamonds are colorless. In reality, however, diamond color ranges from clear to varying shades of yellow and brown. A diamond’s color rating refers to its degree of coloration, and the Gemological Institute of America (GIA) has developed a grading system using alphabet letters D to Z that compares the color of a diamond to the color of pre-selected gems. Later letters indicate deeper colors.

Color Rating Scale

For many stones, the difference between two adjacent letters is minimal and often indistinguishable for casual observers. For Jewelry Lab Certificates and Appraisals as well as insurance purposes, however, the exact grade may be crucial in determining the stone’s value and authentic lab reports are necessary.

• D-E-F: These stones are considered colorless and are the most valuable.
• G-H-I-J: Nearly colorless stones, often colorless to the naked eye.
• K-L-M: Faintly tinted, usually a yellowish cast that may appear gray or brown.
• N-O-P-Q-R: Lightly tinted, yellowish stones. Tint can be seen with the naked eye but may not be noticeable with careful settings.
• S-T-U-V-W-X-Y-Z: Heavily tinted, usually yellow progressing to brown. Tint visible to even when mounted.

Choosing a Diamond Color

Color is a matter of personal preference. Many people may not notice slight shades of color, and lower grade stones are less expensive even when the difference isn’t immediately noticeable. The average color for engagement diamonds is G to H in the United States. The next popular group is J-K-L because they are more affordable. Some people even prefer heavily colored stones because they are more unique in engagement settings.

Investigating Color

You should compare color of the diamond with a ‘reference set’ of stones having known color available at the jewelers’. The diamond in question should be placed face down next to the reference stones on a white piece of paper. The best match would reveal the correct diamond color. If possible, compare the shades under natural sunlight – jewelers may have a special lamp available for this purpose. As a lay observer, however, you may not be able to tell the difference between subtle shades and should compare your estimate with the stone’s certificate.

Improving Diamond Color

It is possible to improve a diamond’s natural color through various laboratory processes. The stone’s certificate should note whether the color is natural or has been enhanced, and reputable jewelers will mention such treatments. For many consumers, artificially enhanced diamonds are a better value because the stone’s cost is primarily set by its natural condition. After treatment, it may appear to be a better grade of stone but the cost will remain significantly lower.

Very low-grade brown or yellow diamonds may be converted to fancy colors by subjecting them to irradiation followed by heat treatment. These colors are usually permanent though they could change if heated to high temperatures during setting repairs. This color treatment, called High Pressure High Temperature Treatment (HPHT), is a controversial process and should be noted on the stone’s certificate.

Most HPHT diamonds are over 0.5 carats and should cost less than comparable natural stones. Larger stones are used for these treatments because many consumers equate value with size, regardless of the stone’s natural condition.

Other techniques can be used to improve a diamond’s color without artificially enhancing the stone itself. Highly-faceted cuts, such as the traditional round diamond or other brilliant cut stones, reflect more light than simple cuts and can create enough sparkle to hide subtle yellow tints. High Engagement Ring Settings have a similar effect, while channel and other sunken settings bring out the stone’s natural color. Accent stones of a higher quality may also help lighten a stone’s color, though if the grades are too disparate the center stone may appear more colored than it really is.