Professional Jeweler Archive: A Worm in the Apple

September 2000

Diamonds: Gemology

A Worm in the Apple

A new internal laser drilling technique simulates natural etched channels in diamond

Some unusual forms of laser drilling are showing up in diamonds at gemological laboratories around the country, and it’s wise for you to know how to spot them because they could involve deception.

Historically, laser drilling involves boring a straight channel from the surface to an inclusion, which then is boiled out with acid, improving the diamond’s appearance. The new technique has the same end goal – boiling out inclusions – but uses a different technique. “What you see under magnification are worm-like channels within a stress fracture or feather,” says Shane McClure, director of identification services at the Gemological Institute of America, Carlsbad, CA.

Tom Moses, vice president for identification services at GIA’s Gem Trade Laboratory in New York City, explains the process this way: “One or more pulsed lasers are focused on an inclusion near the surface to heat it so it expands and creates sufficient stress to extend the cleavage or tension fracture to the surface.” From there, the process is the same: the diamond is placed in boiling acid, which enters through the opening and removes the inclusion.

The Problem

The worm-like channel looks similar to natural etch channels found in some diamonds. “In fact, we first thought they were natural etch channels,” says McClure. “But then we realized these channels were very even, so we knew they weren’t natural.” Unless you know what to look for, you could be fooled into thinking such a diamond is not laser-drilled. Here are several things to look for when examining diamonds:

The new laser technique is used to treat diamonds with inclusions near the surface (extending a deeper cleavage could split the diamond in two).

The treatment seems most prevalent near the crown facet.

The worm-like channels are at the center of a larger stress fracture or feather.

Some channels appear dark in transmitted light.

When light reflects off the surface of a feather, the channels are much harder to detect.

The feather generally appears transparent and glassy under magnification and may be difficult to detect. You may have to change the angle of the diamond and use oblique illumination.

Some of the diamonds show elongated channels that reach the surface. These may be parallel drill holes made to look like naturally etched diamonds.

GIA says it hasn’t seen many diamonds with the “wormhole” channels yet but expects the treatment to become more widespread. Meanwhile, GIA discloses this form of laser drilling in the “comments” section of its diamond grading reports as “internal laser drilling is present.”

– by Robert Weldon, G.G.

The worm-like channels are spotted in the center of a barely visible, glassy, transparent feather that leads to an included crystal. A natural and more visible feather associated with the included crystal is seen to the left of the included crystal.
The irregular channels are often spotted near the crown and star facets. They show up darkly in transmitted light.

Copyright © 2001 by Bond Communications