Detecting New

Laser Drilling Techniques

Characteristics of "Internal"

Laser Drilling By Shane F. McClure, Director of Identification Services, John

I. Koivula, Senior Research Gemologist of GIA Gem Trade Laboratory, Carlsbad,

CA and Thomas M. Moses, Vice President of Identification Services, GIA Gem Trade

Laboratory New York

Background

Until recently laser drilling

has typically been done by boring into the diamond with a fine, narrow, roughly

circular channel to reach a dark inclusion in the interior of the diamond. This

practice has been in place for nearly thirty years. The fine tunnel provided

a conduit to reach a dark appearing inclusion with strong acids that turn the

inclusion from black to a less offensive "white," at the very least minimize

its appearance. The clarity grade may or may not be affected, but in most instances

the diamondÕs salability is improved. This procedure is an accepted trade practice

as long as it is fully disclosed. (figure 1 of traditional laser drilling)

In 1998, both the World

Federation of Diamond Bourses (WFDB) and the International Diamond Manufacturers

Association (IDMA) adopted full disclosure policies for laser drilling. GIA

has disclosed laser drilling on its diamond grading reports since first documenting

the then new process in the early 1970Õs.

Recent

Development

Two new applications of

laser treatment have recently been encountered by the GIA laboratories. As we understand the process, we believe it is done with a higher - powered laser than used in the traditional drilling method. The most suitable diamonds for this procedure are those that have shallow black or dark-appearing inclusions with some type of associated tension-fracture or cleavage. It is our belief that one or more pulsed lasers are focused on the near surface inclusion to heat it so it expands and creates sufficient stress to extend the cleavage to the surface. This now surface reaching fracture provides an entrance for the acids to enter the diamond and bleach the inclusions. We suspect in some cases fracturing caused by the lasering around the inclusion alters its color and minimizes its appearance without the need for pressure boiling or "soaking." This procedure leaves evidence of small channels within the diamond that are usually "worm-like" in appearance and often in the fracture or cleavage plane. In addition, a "glassy" appearing fracture is also present. These fractures may be very transparent and difficult to see in some lighting conditions.

A variation to this process involves cutting a channel into the diamond with what appears to be several drill holes placed side-by-side which end up looking something like a natural etch channel a first glance. Acid bleaching is done through these channels, which are cut to reach internal feathers or dark crystals. In the small number of samples we have seen, this specific procedure has originated near the girdle or in the crown facets. Interestingly, this is also the area where natural etch features are most frequently located. Careful examination with a gemological microscope reveals the dissolution features of the crystal on the faces of natural etch channels in untreated diamonds. Although dull, frosted, or glassy in appearance, the "side walls" of the laser created features do not have the same angular characteristics that occur in natural etch channels

1. This stone shows a typical narrow laser drill hole leading to an included crystal.

2. The effects of internal laser drilling can be seen to the left of this included crystal. The drilling leaves irregular worm-like channels down the center of the glassy transpaent feather created by the process. The original internal feather can be seen to the right of the crystal it surrounds.

3. Some internal drilling channels show a dark appearance when viewed in transmitted light in the microscope. Note that the channels become nearly invisible where light reflects off the feather. This indicates that the channels are actually

4. Instead of the traditional drill hole, this diamond has an elongated channel cut into it that appears to be a series of parallel drill holes. This particular channel has been cut along a star facet junction. Note the uniformity of the hole at the surface.

5. This natural etch feature shows an irregular granular texture on its internal surface.

6. The opening at the surface of the etch feature shown in figure 5 is very irregular, unlike the uniform openings left by laser drilling

Detection

In both instances it is necessary to examine the diamond both in the face up position and holding it table to culet. With the first method of internal drilling, dark-field magnification is most effective for observing the drilling channels and associated features. There are usually one or more small irregular channels, often in the fracture plane, but sometimes adjacent to the crystal. These channels may look dark in transmitted light. The fracture itself usually appears glassy in the areas that it expanded. The entire feature is reminiscent of an expanded included crystal in a heat treated ruby or sapphire. In the second instance, when channels are cut into the diamond to reach the inclusion, reflected light is helpful in determining if the feature is a natural etch channel or was artificially created. Natural features usually have geometric or irregular entrances at the surface of the diamond and the walls of the channel have angular or strongly etched surfaces unlike the channels that have been cut into the diamond with the laser. The channels that are laser induced in the samples we have observed are spike or spicule-like, wider at the surface and tapering down as it nears the inclusion. These channels also have a very uniform straight outline at the surface.

Reporting

To date only a small number of diamonds have been detected with this new type of laser treatment, however, we suspect it will become more prevalent. Currently, these features are disclosed on GIA Grading and Identification reports in the "Comments" with the statement, "Internal laser drilling is present." GIA is continuing to investigate this method to determine its effect on the overall appearance of inclusions and how it impacts the clarity grade. As with traditional laser drilling, we suspect that there will be some "failures" do to the localized shock the diamond receives during the procedure.