By Joe C. C. Yuan -- G.G., D.G.A.

Since the summer of 1994, quite a number of diamond importers, who purchased various kinds of diamonds from international wholesale markets, have noticed that some of the diamonds were fracture filled. The filling skill in the processing has been proved to be more advanced than ever before, all of which were without flash effect or color shade, semi-transparent -- like cicada wings. Such effect had made the feather that should have being graded SI1 to I2 clarity look like VS2 to SI1 .

These diamonds, in particular, are especially favored by the sellers on the recent international markets who made no account that the diamonds had been fracture fill-processed, of which the seller should have made a clear disclosure of the processing. According to the rules of international gem business, the sellers are responsible and obligated to tell the buyers about the filling. However, the sellers never mention a word about the processing. This is, perhaps, because the filling material have such refractive index that it is most close to 2.417, the index of diamond, and that the filling material used in the feathers hardly have presented any color shades. All these features have contributed to the final purchasing of the processed diamonds by buyers, who mistakenly took the filled fractures as some slight, inconspicuous feathers and who also believed that these were a high quality at a lower price.

Considering the fact that people in diamond business that do not know much about the new filling method. The author of this paper had found two pieces of diamond which were already filled by examining them only underneath a microscope. A study was performed to show the evidence that non-color-shade and no-flash-effect feathers has been filled in these diamonds. This experiment was performed by Mr. Yuan, the author, together with Dr. Eugene Huang, and Mr. Chuen-fu Lin, MS, at the Institute of Earth Science under the Academia Sinica in Taiwan. They conducted a scanning test focusing on the feathers of the filled diamonds by using Raman Spectroscopic System. This study was the very first to have used the Raman device to test the material presented in the no flash effect feathers in diamonds.

Raman Spectroscopic System functions by using its optical energy to stimulate the vibration on the material tested. The vibration within its crystal lattice could result in mutual action to generate different scattering lights. When only receiving the Raman scattering light, different materials will have different vibration. By repeat scanning and averaging out the collected data through the computer, we can obtain a more accurate diagram of our object. In the diagram, we look at the position of the Raman peak line and compare it to the Raman spectrum of other known specimen to determine what substances are present in the tested material.


Test the Fracture Filling Material

The Raman Spectroscopic System is now used by taking the argon ion laser as its stimulating light source. The first diamond to be tested was enlarged 100 times under the microscope. The laser beam (with a diameter of 5/1000 mm) then directly focuses on the inside feather, for which we may see the fracture shown in Fig. 1-1. (Before, the whole fracture was semi-transparent. Now the part closer to the surface has melted to a milky white text caused by the heat produced when the author was polishing, while the inner part is still semi-transparent. )

In Fig. 1-2, we can also see the Raman peak lines illustrated: at 1332cm -1, the sharp Raman peak is seen. This is a clear proof of pure diamond (i.e. the carbon). Another wider Raman peak is between 830-930 cm -1, which is the evidence of lead glasses. Furthermore, we did another experiment by directing the laser beams onto the no-fracture part. The result is just as shown like the diagram in Fig. 1-3 which is the pure diamond. Only an extremely sharp Raman peak appears at the position of 1332cm-1.

When the laser beam is directed to the inside of the fractures of the second diamond, the computer-drawn diagram is extremely complicated. This result suggests that the fracture filling material is polymer resin, which has a very wide range of Raman peaks. In order to get a clear peak-valley contrast, by skipping the ultra strong carbon peak at 1332 cm-1, there are several Raman peaks which indicate the filled material polymer resin between 1100 3000 cm-1, except for the three peaks between 2200-2700 cm-1 which is diamond’s double peak.

The Trouble of Fracture-Filled Diamonds

These two diamonds were bought on summer 1996 from different diamond centers. The feathers display the same characteristics -- semi-transparent, with no color shades; yet two different fracture-filling materials were used: lead glass and polymer resin. The seller did not make any disclosure about the filling. It was truly the worst thing that the buyer could not guard against. In addition, the fracture filling substance -- lead glass has its melting point of approximately 300-400°C. It is even lower for polymer resin. Consequently, the filling material can be easily melted and turned into milky white -- during the metal soldering process or diamond polishing. The filled material will disappear in sulfur acid when boiling. This always creates disputes.

This Moment on the Market

In spring of 1998, the author was going to find some no flash effect filled diamonds in the international market again. After two months' efforts, nothing was found. There were many between 1996 to 1997 in every diamond center -- Tel Aviv, Antwerp, New York, Bombay, Johannesburg, and Bangkok.

Until this moment, mid-1999, we can not find this no flash effect filled diamond on the international market. Their disappearance probably due to the pressure from certain organizations toward the treating laboratories.

GIA and HRD do not check fracture filled diamond with Raman spectroscope. They only use X-ray which proven to work effectively while detecting lead glass. However, polymer resin will escape the detection from the X-ray.

Advisory Remarks for Buyers

It is the author's advice to observe the following when purchasing from international wholesale market:

A buyer should beware when he notices the feathers, either big or small, in a whole diamond that are evenly semi-transparent. Or the diamonds in the same parcel exhibit similar semi-transparent feathers. One should ask the seller directly whether the diamond has been fracture-filled. If the seller gives a negative or even hesitating reply, the buyer is entitled to request special testing from a creditable local laboratory for goods to be purchased. If, after the test, the diamond is proven as being filled, the purchasing price should be calculated as the price of feather clarity, when unfilled, plus some filling expenses. As of today, most laboratories will not issue certificate on fracture filled diamonds. It is too early to affirm that the fracture filling processing skills will be finally accepted by the diamond market. It might be possible to be accepted, if we see the situation with other gems, such as the heat treatment of ruby or sapphire, the fracture filling of emerald, and jadeite being bleached by acid and fill with resin. Our best advice is -- it is important for diamond dealers to master the basic detecting knowledge and skills in order to be able to determine whether the diamonds one purchased has been fracture filled.