Diamond Treatments: Fracture Filling, Laser Drilling and More

A diamond treatment is any process, beyond cutting and polishing, that changes how a diamond looks. Treatments are used to make an inclusion less visible, to remove an unwanted tint, or to create a colour that was not there.

Treated diamonds are not fake. They are real diamonds whose appearance has been altered. The essential rule, in law and in good practice, is disclosure: a treated diamond must be sold as treated, and its report should say so.

Two treatments target inclusions:

Laser drilling

A laser bores a microscopic channel from the surface to a dark inclusion, which is then dissolved or bleached so it is less noticeable. A variation opens a natural feather to reach the inclusion instead. The channels are permanent, and GIA grades laser-drilled diamonds, noting the treatment on the report.

Fracture filling

A glass-like substance is forced into surface-reaching cracks to make them less visible. Under some angles the filler can show a flash of colour. It is not permanent: the heat of a jeweller’s torch during repairs, or harsh cleaning, can damage it. Laboratories such as GIA do not issue a full grading report for a fracture-filled diamond.

Other treatments change colour:

HPHT processing

High pressure and high temperature can turn certain brownish natural diamonds colourless or near-colourless, or give them a fancy colour. The change is permanent. GIA reports state it and inscribe the girdle to say the stone has been HPHT processed.

Irradiation and annealing

Irradiation, usually followed by heating, can create greens, blues, yellows, pinks and other fancy colours. The report will state that the colour is treated.

Coatings

A very thin film on the surface can mask a yellow tint or add colour. Coatings can wear, scratch or be removed by cleaning and repair work, so they are the least durable treatment of all.

This guide covers treatments to natural diamonds. Lab-grown diamonds can be treated after growth too, most often to improve colour, and their reports state whether a stone is as grown. Our guide to lab-grown treatments covers those.

Buy a diamond with an independent grading report from a respected laboratory, and read the comments line, where treatments are usually recorded. Check the laser inscription on the girdle against the report.

Ask the seller plainly whether the stone has been treated in any way. A reputable jeweller will answer in writing. Be wary of a diamond whose clarity or colour seems remarkable for its price and that has no report from a major laboratory.

For an engagement diamond, we recommend a stone with no clarity treatment. Fracture filling in particular is not durable enough for a ring worn every day. If a treated stone ever made sense for a design, you would know before you decided, and the report would say so.