Laser drilling is used if there is a large carbon deposit in the heart of the stone, showing as a black speck. A microscopic hole is drilled down to the inclusion and then the impurity is dissolved, usually with Sulphuric acid.
Fracture filling is the process by which these holes and tunnels are filled to hide their presence. This process, which involves the use of specially-formulated glasses with a refractive index approximating that of diamond, was pioneered by Zvi Yehuda of Ramat Gan, Israel. This process is also used to disguise fissures that break the surface of the stone, where no drilling is necessary.
Detecting an enhanced diamond.
A stone that has been fracture filled is greatly enhanced when viewed with the naked eye but to a trained gemologist, the tell-tale signs will be obvious. The tiny holes will appear as dark circles where they break the surface of the stone and as straight white lines within it. The material used to fill the fissures tends to be of a darker colour than the natural stone and this can reduce its colour grade by up to one letter.
Further, a filled stone will sometimes give a coloured 'flash' when turned in the light. This is caused by light reflecting off the plane of the fill material and it tends to be of a distinctive colour. There is an image of a fracture filled diamond here showing the orange flash that gives it away.
Problems with enhanced diamonds.
Views differ within the diamond and jewellery trades as to whether a diamond should be enhanced. The purists tend to think of diamonds as almost sacred and feel that they should be inviolate. Others think that if the appearance of a stone can be improved then, why not?
All agree, however, that such enhancements should be declared and not concealed. The Gemological Institute of America (G.I.A.) refuses to issue certificates for filled stones and other labs downgrade the stones to reflect what they think would have been their original clarity.
There are other problems with enhanced stones when it comes to setting. Often heat is used in the manufacturing or repair of jewellery and, although the diamond can withstand huge degrees of heat, the filling material cannot and often sweats out of the stone leaving its appearance and value greatly diminished.
To buy or not to buy?
Ultimately, if you buy an enhanced stone then you may get something that looks great to the naked eye at a fraction of the price of a stone that has not been tampered with. The main thing is to know. If you know what you're buying and can make it known to any jeweller that might work with the stone then it can be a boon; it's only a bane when you are caught out by not knowing.
The golden rule is: Ask
Click here for information about diamond colour enhancement (the spiel at the foot of that page)
and here for general information on diamonds |
