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April 2007

Contact Angle on Diamonds
This past month I made contact with an old-time ramé-hart customer who has a classic ramé-hart Model 100 NRL Contact Angle Goniometer which he uses to study contact angles on diamonds and other gems. This customer is Martin Haske, an MIT-trained engineer who worked on precision inertial and stellar inertial guidance systems used both in the Apollo and Fleet Ballistic Missile programs before becoming a professional gemologist. Mr. Haske developed the Adamas software used by gemologists to identify and grade gems. He has also developed the SAS2000 Spectrophotometer Analysis System for diamond color grading. He has a passionate interest in learning about and discovering new ways to characterize diamonds and other gems. You can learn more about these advances in gemology at his website: http://www.adamasgem.org/

The idea of measuring the contact angle of water on inorganic minerals as well as different diamond substitutes dates back at least 30 years. In fact, Mr. Haske contacted us in part looking for a copy of an article from the Winter 1977 copy of GEM & GEMOLOGY journal -- which we happened to have in our library. The article reflects the work of Drs. K. Nassau and H. Schonhorn which was conducted at Bell Labs in Murray Hill, New Jersey, during the 1970's.

In their study, they pointed out that diamond substitutes have a contact angle quite different from a genuine diamond, but that irradiation can greatly alter the contact angle by modifying a thin surface layer.

One curious characteristic of a real diamond is that it's hydrophobic -- that is, not easily wetted with water. In the mines of South Africa, they use a primitive but effective separation technique wherein crushed rock is washed with water over a bed of grease. The diamonds will adhere to the grease while the other minerals will wash away.

There existed a need for a way to identify diamonds and distinguish genuine diamonds from look-alikes. The hardness test (using a tungsten carbide point) will scratch everything -- except a real diamond. The other tests included a reflectometer, refractometer, and specific gravity check. Each of these tests have there own limits. So it was proposed that a Contact Angle (CA) test be developed whereby a simple non-destructive measurement could be taken to assist in the identification of diamond and diamond look-alikes.

The test involved the preparation and measurement of CA as detailed in the 6 steps as shown above. The cleaning step was found to be quite important as most of the errors could be traced back to contaminants or films of grease or soap. The test called for a ramé-hart Model A-100. Today this test could be done on a current generation Model 100-F0 or any other model.

The determined CA range for genuine diamond is 47-55° (according to Nassau and Schonhorn). Cubic Zirconia was determined to have a CA from 70-90°. Many other diamond substitutes were found to have CA values higher than 60°. It was discovered, however, that in some cases gems (including diamonds) that had been irradiated exhibited lower contact angles -- which could lead to misidentification. In every case however, these samples -- when polished (to remove the effects of irradiation) and reexamined -- measured as expected. And so, the measurement of CA, it was concluded, can be used alongside other tests to assist gemologists and appraisers in the identification and authentication of diamonds and other gems.

If you are interested in a complete copy of the original article, please contact us.

Announcing New Model 400-F1
NETCONG, NJ - ramé-hart instrument company is pleased to announce the addition of a completely new contact angle goniometer instrument to their product line-up. The new Model 400-F1 is built using proven components from the highly successful Model 200-F1 and Advanced Goniometer 300-F1 and has been specifically optimized with 8" (200mm diameter) rotating wafer support for the semiconductor fabrication market. ramé-hart has long served this market with numerous specialized options. The Model 400-F1, however, marks the first ramé-hart instrument built from the ground up to serve a particular application. Throughout the semiconductor manufacturing process this tool provides an invaluable service in measuring the quality and uniformity of coatings and surface preparations.

The Model 400-F1 ships complete with an 8" diameter wafer support. Other sizes, 4", 6", 10", and 12" -- as well as 6" and 8" vacuum chuck support are also optionally available. Other options include the popular Automated Dispensing System and Environmental Fixture. The system ships complete with DROPimage Standard software, PC, and LCD.

Shown below is the Model 400-F1.

If you would like more information on the Model 400-F1 including a PDF product brochure, a copy of our updated product matrix, or a quotation, please contact us. We would be happy to help you with any other ramé-hart model or accessory.



Carl Clegg
Director of Sales
Phone 973-448-0305
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