A KM-treated diamond is a diamond whose surface-reaching dark inclusions have been bleached or removed by the KM process, a laser-assisted acid clarity treatment introduced commercially by the Israeli company KM Diamond Equipment in the early 2000s and now adopted under various trade names by several manufacturers. The treatment is sometimes catalogued under the more general industry label LDI, for laser-drilled inclusion treatment, but KM has become a generic shorthand in trade speech for any laser-assisted, surface-reaching clarity enhancement that does not leave a visible drill hole. For a treatment of the underlying process, see the related entry on KM treatment.

What the stone looks like under inspection

KM-treated diamonds are distinguished from traditionally laser-drilled diamonds by the absence of a clearly visible cylindrical drill channel. Where conventional laser drilling leaves a fine, glassy tube reaching from the surface to the inclusion site, KM-treated stones present instead an irregular, fissure-like channel or a series of feather-like surface-reaching planes that have been opened by laser energy and then chemically bleached. Under high magnification the treated zones often resemble natural feathers or cleavages, which is the source of much of the dispute around disclosure of this treatment. The bleached former inclusion site may appear as a faint white, hazy or translucent area, sometimes containing residual filling, in contrast to the clean, glass-clear residue of a true Yehuda or Koss fracture-filling.

Disclosure and grading

The GIA grades KM-treated diamonds and reports the treatment under the heading clarity enhancement, with the comment that the stone has been treated to improve apparent clarity. The Federal Trade Commission Jewelry Guides require disclosure of any treatment that materially affects value, and the AGTA, the World Jewellery Confederation and Canadian Jewellers Association codes likewise require disclosure of any laser or chemical clarity enhancement. KM treatment is generally regarded as stable for ordinary wear and does not require special handling at the bench, but a treated stone retipped under heat without protection may darken at the treatment site as residual chemistry oxidises.

Trade and pricing

KM-treated diamonds typically trade at a substantial discount to untreated stones of equivalent post-treatment appearance, often in the range of 30 to 50 per cent of the equivalent natural-clarity Rapaport, varying with size and the visibility of the residual treatment trace. The discount is similar to that applied to traditionally laser-drilled stones and reflects both the disclosure obligation and the absence of a meaningful resale market at full price. For Toronto retail, KM-treated material is most often encountered as melee in price-led mass-market mountings; care should be taken at intake of estate goods to identify the treatment, since it is easily missed without ten-power loupe inspection of the surface in a well-lit examination.

Distinction from fracture-filled diamond

KM-treated diamonds are sometimes confused with fracture-filled diamonds of the Yehuda or Koss type. The two treatments are distinct: fracture filling injects a high-refractive-index glass into a natural feather to mask its visibility, while KM treatment opens and bleaches the inclusion site rather than filling it. A fracture-filled diamond will show the characteristic flash effect, a brilliant orange or pink streak along the filled fracture under tilt, that a KM-treated diamond will not. The two treatments are reported separately on GIA documents, and are subject to separate disclosure standards in the AGTA and CIBJO codes.