The Federal Trade Commission’s Guide for the Jewelry, Precious Metals and Pewter Industries

FTC writes:

23.13 Disclosure of treatments to diamonds.

A diamond is a gemstone product. Treatments to diamonds should be disclosed in the manner prescribed in 23.22 of these guides, Disclosure of treatments to gemstones.

More info @ http://www.ftc.gov/bcp/guides/jewel-gd.htm