Treated Diamonds: HPHT, Laser Drilling and Fracture Filling Explained

Treated diamonds are natural stones altered to improve colour or clarity. HPHT, laser drilling and fracture filling explained, with the effect on value.

Treated diamonds are natural, mined diamonds that have been altered after cutting to improve their colour or clarity. They are not laboratory grown and they are not imitations. They are real diamonds that have been helped along, and the help changes their value. Every reputable laboratory discloses treatments on the report, and every reputable seller discloses them at sale. The three treatments a buyer is most likely to meet are described here.

HPHT: high pressure, high temperature

Some natural diamonds are brown because of distortions in their crystal structure. Subjecting such a stone to very high pressure and temperature, similar to the conditions in which it originally formed, can relax those distortions and turn a brown stone near colourless, or in some cases produce pink, blue or yellow.

What it does. Improves colour, sometimes by many grades. The change is permanent and stable.

How it is detected. Not by eye, and not with a loupe. Laboratories use spectroscopic analysis. A stone with an HPHT treatment will be marked as such on the report and typically inscribed on the girdle.

Effect on value. Substantial. A treated near colourless stone sells well below an untreated stone of the same grade. It is honest and durable, but it is a different product.

The risk. Undisclosed HPHT is the treatment most likely to slip past an unwary buyer, because the stone looks exactly like an untreated one. The only protection is a report from a laboratory with the equipment to detect it.

Laser drilling

Dark crystal inclusions can be reached by drilling a channel from the surface with a laser, then dissolving or bleaching the inclusion with acid. The dark spot becomes a white one, which is much less visible.

What it does. Improves apparent clarity by making dark inclusions pale. The drill channel remains and is itself an inclusion, usually noted on the plot as a fine line.

How it is detected. Under magnification, the channel is visible as a straight, narrow tube running from the surface to the treated inclusion. Some newer methods create internal fractures rather than a straight channel and are harder to see but still detectable.

Effect on value. Meaningful. Laser drilling is permanent and does not weaken the stone in normal wear, but the stone is worth less than an undrilled one of the same resulting grade. Laboratories will grade a drilled stone and note the treatment.

Fracture filling

Surface-reaching feathers and fractures can be filled with a glass-like substance whose optical properties are close to diamond. The filled fracture becomes far less visible, sometimes lifting the apparent clarity by two grades.

What it does. Hides fractures. It does not remove them and does not strengthen the stone.

How it is detected. The filler often shows a flash of colour, typically orange or blue, when the stone is tilted under magnification. Trapped bubbles and a slightly cloudy texture in the filled area are other signs.

Effect on value. Large. Fracture filling is the least accepted treatment because it is not permanent. Heat from a jeweller's torch during repair, ultrasonic cleaning, or strong chemicals can damage or remove the filler, and the fracture reappears. Some major laboratories will not issue a full grading report for a fracture filled stone.

The practical hazard. A jeweller who does not know a stone is filled can ruin it during a routine resizing. Anyone owning a filled stone should tell every jeweller who handles it.

Disclosure and the report

Treatments must be disclosed under the standards of every major trade body. A laboratory report states them in the comments, and the absence of a comment on a report from a reputable laboratory is reasonable evidence that no treatment was found.

A stone sold as clarity enhanced is a treated stone. The phrase is a disclosure, not a feature.

Buying one knowingly

There is nothing wrong with a treated diamond bought at a treated diamond's price. HPHT and laser drilled stones are stable and wear normally. Fracture filled stones need care. The problem is only ever a treated stone sold as untreated, and the defence against that is a report from a laboratory equipped to tell the difference, matched to the stone by its inscription.

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C'Garden is an independent bespoke jeweller in Kuala Lumpur. We are not affiliated with, endorsed by, sponsored by or certified by any organisation, laboratory or brand named in this article. Third-party names are used only to refer factually to those organisations and their published standards. All text and imagery in this article is original work created by C'Garden.

Reference

Gemological Institute of America. (n.d.). Diamond treatments. GIA. https://www.gia.edu/diamond-treatment