16 CFR 23.24: Disclosure of treatments to gemstones.

It is unfair or deceptive to fail to disclose that a gemstone has been treated if:

(a) The treatment is not permanent. The seller should disclose that the gemstone has been treated and that the treatment is or may not be permanent;

(b) The treatment creates special care requirements for the gemstone. The seller should disclose that the gemstone has been treated and has special care requirements. It is also recommended that the seller disclose the special care requirements to the purchaser; or

(c) The treatment has a significant effect on the stone's value. The seller should disclose that the gemstone has been treated.

Note to § 23.24:

The disclosures outlined in this section are applicable to sellers at every level of trade, as defined in § 23.0(b) of these guides, and they may be made at the point of sale prior to sale, except that where a product can be purchased without personally viewing the product (e.g., direct mail catalogs, online services, televised shopping programs), disclosure should be made in the solicitation for, or description of, the product.