What is the 5th C in Diamond Grading?

By Robert Underhill


The Fifth C in Diamond Grading

Now that you think you know everything there is to know about diamond grading, there are still a host of things that do not fall into the categories of the "4-Cs".


Diamond Fluorescence

One of the phenomena a diamond can exhibit is fluorescence. Fluorescence in a diamond can be detected by using a black light. When viewed under a black light, fluorescent diamonds will glow with varying intensities and in varying colors. Diamonds that have higher grades of D through H can be significantly lower in value if they exhibit strong fluorescence, as this will detract from the appearance of the stone. Diamonds with lower colors J and below are often more attractive if they have a strong blue florescence.


Diamond Treatments and Enhancements

Diamonds are subject to many different types of treatment that effect their color and clarity. The accepted standard for a treated diamond is that any process that alters their natural characteristics should be disclosed to the consumer.


Diamond Clarity Altering:

Diamond Laser Treatments

One common treatment is laser drilling. Lasers can be used to bore small tunnels into a diamond to burn dark, undesirable inclusions from the stone. The vented areas can then be treated with acid to whiten the areas formerly occupied by "carbon" spots.

This process should be disclosed to the consumer. However, many consumers are unaware that this modification was made to their diamond. Laser drilling is detectable under magnification and usually does not compromise the durability or change in appearance over time.

Note: This process should not be confused with laser inscribing a stone’s girdle with a serial # or message, which is an acceptable practice.


Diamond Fracture Filling

The most common clarity enhancement today is fracture filling. In this process venting inclusions and fractures are filled with a foreign material that is cured or hardened in the stone. Once the fractures are filled, the diamond appears to have fewer or less noticeable flaws.

This process must be disclosed to consumers; that a foreign material has been added to the diamond. None the less, it is not uncommon to encounter a consumer who is unaware of the treatment to their stone. Clarity enhanced diamonds trade at dramatically lower prices than their similar natural counterparts. The concern with this treatment is that the fill material may expand and contract at different rate than the diamond, potentially altering the stone’s outward appearance over time, or during cleaning or ring sizing.


Color Enhancement:

Diamond Irradiation

Diamond irradiation has been used for decades to alter the color of diamonds. This process is most commonly used to add a desirable color to the diamond: blue, green, yellow, etc.
Once again it is required that irradiation be fully disclosed to the consumer. Irradiated diamonds trade at significantly lower prices than natural, fancy, color diamonds. Irradiated diamonds may also shift in color when heated in normal jewelry repair.

Diamond HPHT Treatments

High pressure, high temperature treatment can alter the color of a diamond to make it more colorless, or to add fancy color to a diamond. The treatment is very difficult to detect.