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GIA Identifies New Laser Drilling Treatment
Apr 17, 2000 12:29 PM
By Shaun Gatter
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(Rapaport…April 17, 2000) The Gemological Institute of America (GIA) reports that its Gem Trade Laboratory has discovered a new laser drilling treatment that does not have the surface-reaching drill hole traditionally associated with laser drilling.
In traditional laser drilling, a hole drilled to a dark inclusion in the interior of the diamond serves as a channel for the strong acid used to remove or minimize the dark material. According to Thomas Moses, vice president of Identification Services for the Laboratory, "The most likely candidates for this new procedure are diamonds that have shallow black or dark-appearing inclusions with some type of associated tension-fracture or cleavage."
The new laser treatment leaves no surface drill hole. "One or more pulsed lasers are focused on the near-surface inclusion to heat it so that it expands and creates sufficient stress to extend the cleavage to the surface," explained Moses. This provides a conduit to the dark inclusion for a treatment that most likely involves boiling (often with pressure) in strong acids to reduce the visibility of the dark inclusion. The lasering leaves evidence of one or more internal channels within the cleavage or adjacent to the inclusion, but there is no surface-reaching drill hole.
Moses also noted a variation of the new laser process, which involves, "cutting a channel into the diamond with what appear to be several drill holes placed alongside each other. At first glance, this could resemble natural etching. Acid bleaching is then introduced through these channels, which have been cut to reach internal feathers or crystals."
When a traditional laser drill hole is present, GIA policy is to note it as the first item in the Key to Symbols of the Diamond Grading Report. According to Moses, when features associated with these new lasering techniques are detected, GIA states in the "comments" section of its Report: "Internal laser drilling is not shown." On a Grading Report, this comment, which alerts the customer to the presence of laser drilling, is in place of a symbol on the plotting diagram. Evidence of this new treatment has been found in only a small number of stones. The GIA research is ongoing.
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Tags:
GIA
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