Diamonds make a perfect treatment target

Posted July 01, 2013 |

Advances in technology demand that jewellers keep up to date on the variance and prevalence of gemstone treatments. This is especially true when it comes to diamonds, the world’s most sought after gemstone.

The consistent market value and popularity of diamonds make them the perfect target for unscrupulous dealers looking to take advantage of the public and the industry.

Treatments of diamonds are intended to enhance the colour and clarity of the gems and are designed to be as imperceptible as possible.

Furthermore, the dizzying array of treatments is now compounded by the arrival of synthetic diamonds, but jewellers should take confidence from the fact that many treatments are easily detectable with a loupe, a lint-free cloth and a healthy quantity of natural light.

Fracture-filling with a special type of glass. Inset: laser drilling is reserved for large, dark inclusions

Assess every stone that comes across the bench, whether it arrives with a certification or not because someone may have missed an important feature in their assessment. Or perhaps the stone has been shipped with the wrong cert? Always check stones against the accompanying certificates to avoid costly or embarrassing mistakes.

Imagine having to replace a one-carat diamond that was destroyed during a ring resize because you didn’t know it was glass-filled.

Diamond treatments can be as simple as a drop of indelible ink on the culet or around the girdle. Often these inks have a slight bluish tint, which counteracts the yellow colour of the diamond, making the appearance of the diamond seem more colourless. They can be easily indentified on closer inspection with a 10x lens.

One common treatment is fracture-filling. Crevices and fractures that reach the surface of the stone can be filled with a special type of glass or glass-like substance that has a refractive index similar to that of a diamond.

When the fracture is filled, it diminishes the visibility of the fracture, enhancing the clarity.

This filler can have a low melting temperature so any significant heat from a blowtorch, steam or ultrasonic cleaning can melt or damage the filler.

Again, fracture-filled diamonds can be detected with a 10x lens and an experienced eye (see larger image).

Another common treatment of diamonds is laser drilling. Often this practice is reserved for large, dark inclusions. This process uses the concentrated intense heat of lasers to vaporise a tiny tunnel to a particular inclusion, without fracturing or damaging the stone (see inset image). The hole that has been created is then filled with acid to bleach out the inclusion, significantly increasing the clarity of the diamond.

A 10x lens can pick up the tiny drill holes in the surface and the line to the inclusion; however, techniques are now being developed where diamonds can be laser-drilled, obliterating the inclusion without breaking the surface of the stone. Laser drilling must be disclosed to clients as it lowers the clarity grade.

The colour of diamonds can also be altered using irradiation and heat. These processes alter the crystal lattice within a diamond to modify the colour.

HPHT (high pressure, high temperature) diamonds are subjected to conditions of intense heat and pressure that mimic the natural conditions in which the diamonds form. This also creates the shift in colour through changing the atomic structure. If these treatments are suspected, these stones should be sent to have full laboratory testing.

Any of the above treatments can be combined, meaning that jewellers should always be on the lookout for all of them.