Translated from a Japanese paper in Volume 7 of 8 of Gemmology
The story of my meeting with Mr Gilson starts from the hijack.
On 18th July 1973, I visited Mr Pierre Gilson of Gilem Co in Geneva by my clients Mr Naftule’s introduction. My travel purpose was to see his newly developed experimental synthetic opals.
Next day, I left Geneva with a sample of these Gilson opals. Just after our JAL jumbo plane took off the Amsterdam Airport toward Tokyo, the plane was hijacked by five Arabian Guerrilla group (including one Japanese). After spending three days and three nights in the plane at Dubai, finally the plane landed in North Africa and all the passengers and crew were escaped by chutes. Then the hijackers blew up the plane. All the passengers had to leave the plane without any belongings so my samples and data from Gilem Co were burnt together with my other luggage.
But after this incident our company started doing synthetic emerald and opal business with Gilson Co. Annual figure was about US$100,000. Sooner or later, in about 1980, our relations grew to such an extent that we purchased Gilson Co.
The theory of opals’ play of color
In 1964, Australian scientists Drs Darragh, Sanders and Gaskin informed the world of the theory of opals play of color. By studying opal with the electron microscope they discovered that the play of color was caused by the orderly arrangement of the amorphous (non-crystalline) silica spheres (200-300nm diameter) arranged in a regular pattern.
The distance between spheres is shorter than the wavelength of visible light. The white light comes in from one direction and when it reaches the stacked silica spheres, it is deflected at many angles. These diffracted beams of light shows the different spectral colors that look like a rainbow.
Manufacturing process for synthetic opal
Mr Pierre Gilson started to study synthetic opals based on the information published by Dr Darragh and others thesis. In 1972, he succeeded in synthesizing opals, and two years after in 1974 Pierre Gilson started to sell this man-made opal to the public as Gilson Synthetic Opal. In the first place, white opals came in the market. Black opals followed next and subsequently he succeeded in producing transparent crystal opals (water opal). These synthetizing method involve a kind of flocculation method.
First, you add a little ethyl silicate into boiled weak alkaline solution and colloidal silica will grow. After separating and eliminating the condensed coarse spheres, by a sedimentation method, you drip ethyl silicate through a cooling installation and you grow amorphous silica spheres using colloidal silica as seed. You need a few months to get growth of uniform spheres and also you have to check the growing spheres all the time by a spectrometer. For this purpose, checking and modifying the temperature, density, and pH of the solution is very important. You stop the dripping of the ethyl silicate when sphere diameter becomes around 550nm. Then you continue to boil them a few more days and the effects are concluded.
After you collect and remove alcohol by distillation, you transfer the suspending solution, which contains the grown-up spheres into the clear container, such as a beaker. Then you let them settle down quietly over a long period of time. It takes a few months for the spheres to settle into a regular pattern. Centrifugal force cannot be used to accelerate settling of spheres. A few months later you will see the play of color displayed by the settled spheres in the beaker.
After you aspirate and remove most of the upper solution, you must add some more fluid containing colloid silica and stir the spheres up then for a second time to allow settlement start. First, settled spheres in the beaker become the cores and the later settlings grow upward as columns. At this time, the superior column eliminates the inferior column. In mineralogy, we explain these as geometric selection (Grigorlev 1965) and honeycomb color patterns get larger and larger.
The settled spheres exist in gel conditions and moisture is only slowly removed by natural evaporation so that dryness takes a long time. The gel turns into solid condition by the heat treatment until the gel becomes silica-stacked spheres of amorphous silica. Under this process, you can make black opal and transparent crystal opals by adding several additives. It takes about one year for the whole process.
Character of Gilson synthetic opals
The characteristics of natural opals are varied and depending upon where they come from. The composition of both natural and synthetic opals are generally the same, of course, it is silica. The specific gravity of synthetic opal is little higher than natural opal. The reason seems to be due the difference of water content. Hardness of synthetic opal is slightly higher than natural ones. The refractive index of both opals are almost the same. Gilson synthetic opals play of color is very clear and beautiful.
Some times very good quality synthetic opals are equal in beauty to that of natural ones. Gilson synthetic opals spheres grow vertical in the bottom of the container with the columnar structure forming by natural settlement. While growing, the angle of columns will change from one to other column because of the principal of ‘geometrical selection’.
These differences in the angulation of columns in Gilson synthetic opal may explain why you can observe the ‘lizard skin’, when you observe them in their vertical angle of growth. If you cut Gilson synthetic opal according to the vertical angle of color pattern growth direction and polish them, you can observe the typical honeycomb structure, which is called ‘lizard skin’ under the optical microscope. This is the distinctive feature of synthetic opals from the naturally occurring opals.
The present conditions of synthetic opals
Mr Pierre Gilson talked of his dream to me, showing his experimental Gilson synthetic opal necklace. He said he wanted to ornament women’s neck all over the world with his opal necklace. He asked me to introduce him to a pearl manufacturer because he was investigating the equipment of the grinding synthetic opal to round and making center hole. These things he didn’t carry into effect.
1980 Gilson Co sold manufacturing equipment and technology of synthetic opals to a Japanese maker and they continued productions by Tajil Co in Switzerland, which is the Swiss office of Japanese Arce Medium Co. But sales were not so good as they expected. Arce Co tried to manufacture them in Japan also, but they only manufactured on a trial basis and then Tajil and Arce both stopped manufacturing. At present only Kyocera (Kyoto Ceramic) Co is manufacturing synthetic opals, making jewelry and selling with their own brand name in Japan.
Mr Nakazumi
Gemmology Queensland Volume 6 / No 4 / April 2005
No comments:
Post a Comment