By Yehuda Yakar, GG GIA, Chief Gemologist at GCI
|Yehuda Yakar, GG GIA, Chief Gemologist at GCI|
All natural diamonds have faults that could negatively influence their gemological rating and financial value. Diamond cutters can remove some of the clarity faults, but some flaws demand a different treatment, one which has techniques developed since the 1970s to nowadays. Every treatment that a diamond undergoes must be disclosed at every stage. Anyone who violates this obligation is breaking rules which apply to members of every diamond bourse and association in the world. In some cases, it is even illegal not to disclose.
According to a decision made by diamond industry regulatory agencies, the clarity level of diamonds is determined in accordance with what is observed at ten-fold magnification. Faults that cannot be seen with the naked eye at this level of magnification will not be taken into account when the clarity level is determined. Diamond flaws are divided into two main categories - internal flaws (inclusions) and external flaws (blemishes) which occur naturally or result from the manufacturing process.
Common inclusions include crystal bubbles, coal spots, clouds, cracks, distortions in the crystalline structure and translucency in the diamond. The most common blemishes include faults that occur during the manufacturing process, scratches, worn down points, extra facets and more.
In a series of articles we will examine common treatment to improve the clarity and appearance of diamonds.
Starting in the 1970s, diamond manufacturers and dealers used lasers in order to drill tiny holes in diamonds. The widths of these holes are thinner than human hair (less than 100 microns). The technique is used to remove or reduce dark bubbles by whitening them, using acids and heat. This is meant to increase the marketability of the diamond. Sometimes, although the technique hides existing bubbles, or causes them to be less obvious, the laser drilling does not improve the clarity level of the diamond. In fact, the drill hole end up affecting the diamond's clarity level.
Steps in the Process
1. Focusing a very powerful laser ray on the bubble in the diamond
2. The laser ray creates a small passage towards the bubble using heat (from the bubble outwards)
3. The bubble is transformed to a white color using hydrochloric acid, which is injected into the passage at a temperature of 300 degrees Celsius using very high pressure
It's possible to identify a diamond that was drilled with a laser by checking it carefully with a microscope or a 10X magnifying glass. Sometimes greater magnification is required. In a diamond that has been drilled with a laser, one can see the drill passage that was created using the laser ray. Most of the drilling is done in the direction of the table, which reduces their visibility. On the table one can see small dots which are the result of drilling. A very small laser drilling, or one that is short or hidden from sight by its mounting, may be very difficult to identify.
The World Federation of Diamond Bourses (WFDB) obligates members of diamond bourses all over the world to disclose. The gemological labs will indicate that fact that a diamond was drilled in a document and the hole opening will be noted in the gemology certificate as a clarity characteristic.
Internal Laser Drilling
Internal Laser Drilling (ILD) is a variation on laser drilling. As far as we know, the technique was developed in Israel at the end of the 1980s. Using this technique, black protrusions are removed using one (or more) laser rays in order to widen an existing crack, or a series of cracks inside the diamond, and in this way to release the protrusions during the lasering. The different between normal laser drilling and special drilling is that normal laser drilling uses a symmetric round hole between the protrusion and the surface of the diamond - table, sides or point, the closest of these to the protrusion. The tip of the drill creates a passage directly towards the inclusion. With the KM technique, there is no drill passage, and it does not reach the outer surface. The treatment creates a series of fractures that reach the surface, through which the acids will later enter and clean out the protrusion.
1. The special drilling allows for the insertion of the white solution that absorbs and brightens dark faults in the stone, and causes them to become less visible.
2. The process is intended to remove the black inclusions from the stone without making the passage created by the laser ray drilling visible. As a result, the crack created by the process looks more natural than a hole that was drilled using traditional laser drilling.
The fault that previously existed in the stone has grown.
Steps in the Process
1. A semi-focused laser ray creates heat which causes the existing crack to widen and reach the surface, or to open up a passage to another existing crack that reaches the surface.
2. Inside the stone, the crack meets the bubble that must be lightened or melted - this is the reason that these kinds of cracks are always located directly above the bubble.
3. After the treatment has been applied with a laser ray, the stone undergoes deep boiling in order to clean and whiten the black faults.
This kind of treatment is harder to identify than regular laser drilling, because after the treatment, the crack looks natural. Under a microscope, a diamond that has received ILD treatment reveals a series of small graded cracks that show signs of scorching. These passages, which look like wormholes or fish's teeth, are clear indications of this type of treatment.
The World Federation of Diamond Bourses (WFDB) obligates members of diamond bourses all over the world to disclose. The gemological labs will indicate that fact that a diamond was drilled in documentation.