KM treatment is a laser-assisted acid clarity enhancement of diamond developed and commercialised by KM Diamond Equipment of Ramat Gan, Israel, in the early 2000s. It is one of a class of internal laser treatments designed to remove or bleach dark inclusions in diamond without leaving the visible cylindrical drill channel of conventional laser drilling. The KM acronym is widely used as a generic trade term for the technique, in the same way that Yehuda is used for fracture filling.

Process

Conventional laser drilling, in use since the 1960s, bores a fine tube from the surface of a diamond down to a dark inclusion, which is then dissolved or bleached with acid introduced through the channel. The resulting drill hole, while extremely fine, is detectable under ten-power loupe inspection as a glassy tube and is required to be disclosed. KM treatment substitutes a shorter, controlled laser pulse that exploits an existing natural fracture or pre-existing tension plane in the diamond, opening the fracture from the inclusion outward to the surface rather than driving a new channel into clean material. Acid is then introduced through the now-opened plane to bleach the dark inclusion, leaving a treated zone that resembles a natural feather rather than a manufactured drill hole. Variants of the technique sold under names such as KM Channel and KM Internal differ chiefly in the laser pulse profile and in the degree to which the fracture pathway is exploited.

Detection

Detection of KM treatment requires careful loupe and microscope inspection at the bleached inclusion site. Indicators include a feather-like or fissure-like channel reaching from the surface to a former inclusion, a hazy or whitish residue at the inclusion location, and surface markings on the crown or pavilion at the entry point of the laser energy. Under proper transmitted lighting the treated channel often shows as a translucent, slightly cloudy plane, distinct from the clean glassy residue of a Yehuda fracture filling. The GIA, IGI, AGS Laboratories and HRD all detect and report the treatment as clarity enhancement on their grading documents.

Disclosure

Disclosure of KM treatment is required under the Federal Trade Commission Jewelry Guides in the United States, the Competition Act and the related Jewellery and Precious Stones marking standards in Canada, and the equivalent CIBJO Diamond Book provisions internationally. The AGTA Code of Ethics requires disclosure to the consumer and at every level of the wholesale trade. Failure to disclose KM treatment is the principal regulatory issue around the technique, and several enforcement actions in the United States and India have addressed undisclosed KM-treated parcels passed off as natural-clarity goods.

Trade position

KM treatment is most commonly applied to small commercial-grade diamonds, melee through one-carat sizes, in which the cost of the treatment is justified by the visual upgrade. Larger stones are occasionally treated, but the disclosure and resale discount tend to make the economics less attractive at the high end. The discount applied to KM-treated material in the wholesale trade is broadly similar to that for traditionally laser-drilled stones, generally 30 to 50 per cent of the equivalent untreated Rapaport.