Opal Information

Faceting takes a lot more expensive equipment, is more difficult to learn, takes a lot of time, and in most cases the efforts are not rewarded because the job is already being done very cheaply by large well organized factories using cheap Labor. You could spend days perfecting a sapphire facet, only to find that you could buy the whole stone for a few dollars from Thailand. To a degree, the same thing applies to cabochons, but the difference with opal is that much of the rough available from Australia is not available to large manufactures. It is still much a family orientated industry and the average person like you or I can still find a little niche in the industry and without too much effort, produce some very good quality gems either for personal apparel of for resale.

Another thing about cutting a cabochon is that it is a process that really just enhances the natural colors in a stone. Particularly in the case of opal, the play of color has already been completed by nature, whereas, in the case of a white diamond, sapphire, or topaz or example, the play of color is developed by the application of facets. If it were not for interference by man, there would be not color in these stones at all. They would resemble common glass. Cabochon cut opal is different. The color is already there. The cutter just shapes and polishes it.

Definitions

Note: There are quite a lot of differences between the Australian and American ways of spelling. I have opted in most cases to using the American, since most of my business is done in that country,. . and my word processor speaks American and keeps telling me that I’ve made a mistake…so I’ve decided to go along with it. Also keep in mind that for every suggestion made about gem cutting procedure, there will be someone who disagrees with it. If you think you’ve got a better suggestion, or would like to put your point of view, please take advantage of the chat program on the www.opalmine.com Internet site, or just send an e-mail to me (Peter): peter@opalmine.com I’m always open for new ideas or suggestions to pass on to the ever-increasing family of Gem Cutters, the world over.

Unless you understand the various terms associated with the movement of light, you will not understand how various opals are identified and put into different categories or groups. Sometimes, we use terms that we think we understand but when it comes down to definitions, we really do not. For example:

Opal: (½p…l) n. 1. A translucent mineral of hydrated silica, often used as a gem. [From Sanskrit upala¡.] (This means you can quite often, but not always, see right through it)

Latin: ‘opalus’ to see a change in colour. Chemically, hydrated silica similar to quartz.

Terms often associated with opal:

a. Opalescence: Having a play or “show” of colors similar to an opal.

b. Opaque: Not letting light through. Not transparent. Dense.

c. Amorphous: Shapeless. Not consisting of crystals. Non crystalline. Glass is amorphous. Sugar is crystalline.

d. Silica: (Silicon Dioxide) A hard, white or colorless substance, that in the form of quartz, enters in to the composition of many rocks, and is contained in sponges and certain plants. The needle in the mouth of a female mosquito is made of silica. Flint, sand, chalcedony, and opal are examples of silica in different forms.

e.Hydrate: A compound produced when certain substances chemically combine with water.

f.Translucent: Letting light through without being transparent.

g. Transparent: Easily seen through.

h. Incandescent: Glowing with heat (red or white hot) as in a light bulb which glows white hot, but produces a light that more closely simulates natural sunlight which is more conducive to bringing out the natural colors in opal.

i.Fluorescent: A light produced by the electrical stimulation of a gas or vapor. (I.e.. fluorescent lights which have a similar effect on opal as a bright cloudy day. Not so conducive to showing the colors in opal).

j. Deflection: From ‘deflect’. (to turn aside, to bend) The bending of rays of light from a straight line.

k.Diffraction: From ‘diffract’. (to break in pieces) A breaking up of a ray of light into either a series of light and dark bands, or into colored bands of the spectrum.

l. Diffuse: To spread out so as to cover a larger space or surface. To scatter.

m. Spectrum: The band of colors formed when a beam of white light passes through a prism, or by some other means. (e.g.. mist or spray, in the case of a rainbow) The full range of spectrum colors is red, orange, yellow, green, blue, indigo and violet.

n. Sphere: A round geometrical body whose surface is equally distant at all points from the cent

Lighting & Color

As an opal dealer, you will want to flatter your stones and present them in their best dress so as to speak. Use either ordinary incandescent lights, (such as a bed lamp or office lamp) floodlights, or if you want to keep the heat down, a 12v lighting system. Not fluorescent lights. (There are some exceptions to the rule. Some feel that some opals show up better in half light or in fluorescent lights. This of course is a matter of opinion, but as a general rule, incandescent lights are recommended