Using Computer Tomography in Diamond Cutting

November 2003

The blank walls of Antwerp’s diamond district cover a vast variety of activities, from traditional trading practices to the most advanced applications of fine technologies. A visit to one of Antwerp's leading diamond cutting centres was in that respect a true eye-opener. This was the work of two companies: the mother company developed an important part of the technology used for the service activity and the other added the unique x-ray computer tomography (CT) scanning optimized for diamonds. Together they considerably enhance profit for the rough stones they buy.

The objective is to optimize cutting solutions for large diamond crystals. At present its optimization is 15 to 20% better than other approaches.

These methods of advanced technology are used only for stones of high quality and substantial size, i.e. above 5 carats(1 carat = 0,2 gramme, 1 point = 0.01 carat ), for which they are of particular importance and which justify the relatively high cost of this type of investigation. More traditional investigative techniques are also carried out where appropriate.

The research involved in optimizing the CT technique for diamond began in 1998 as an IWT (Institute for Science and Technology) project with the VisionLab research group at Antwerp University. The microCT-scan used, although similar to its medical counterpart, is one million times sharper. This very high resolution CT-scan results in a three dimensional digital model of outlines and particular inclusions, with, at present, an imaging precision between 10 and 30 microns depending on the size of the rough stone. The research team aims at further refining the CT technique. They recently conducted experiments at the ESRF (European Synchrotron Facility) in Grenoble (France). They are looking for a way to detect included diamond in diamond, which lack X-ray absorption contrast and therefore are difficult to measure.

The CT-scan is at work 24 hours a day. Progressing in steps of 30 microns it will work its way through a 5 carat stone in 3 to 4 hours, though efforts are made by the researchers to reduce expertise time.

The different production steps are technology supported. The complex software developed on-site by the research team includes light-path simulators to ensure the highest brillliance. It also has a continually updated record of market values for different shapes, sizes and grades, so that the calculated value of the models leads to commercially optimal solutions.

Given these finely calculated data, the diamond experts will make the final decision of cutting styles and shapes, and the computer will issue a precise instruction sheet to the cutters. The present error margin between the calculated data and the cut product is already of a phenomenal precision: one point only.

The largest cut stone they manufactured is over 90 carats, of top colour and clarity grade.

Brigitte Revol MacDonald

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