- Star Resulting From Selective Absorption
- Star Phenomena From Interference Light
- Distinguishing Star Gemstones
One point relating to the identification of gemstones that is emphasized in the GIA courses is the danger of making identifications by sight alone. However, those gemstones that exhibit some of the unusual reactions on light described in this assignment are sometimes so distinctive in appearance as to permit sight identification.
For example, the play of color seen in opal is not duplicated in any other gemstone nor effectively in any imitation; the only effective substitute is a double made from a thin piece of fine-quality opal cemented to a supporting piece such as chalcedony.
Labradorite, a stone that finds little use as a gemstone, displays a change of color that is seldom confused with that of opal, since, unlike the usual tiny mosaic of different colors in opal, the colored light is reflected from thin plates of UNIFORM thickness and the color is confined to ONE hue over large areas.
The only important substitutes for natural phenomenal stones are milky-white chalcedony, often sold as "moonstone"; asteriated rose quartz with a colored-foil backing; synthetic corundum or spinel with fine lines engraved on the flat back of the cabochon and backed by metal foil to create a star effect; synthetic star sapphires and rubies; and the poor glass imitations of opals, stars and cat's-eyes.
In general, these substitutes, are detected readily by their lack of re-semblance to the natural stones they represent. Opal doublets, unless mounted in a gypsy-type mounting, are detected easily by the obvious separation between the thin pieces of natural opal and the rough backing material.
Foilbacks used to imitate star sapphire and ruby were once limited to rose quartz that displayed a weak star without foil backing. Red and blue foil imparts a deep ruby and sapphire color only when star-quartz foilbacks are viewed from above. Looking through the cabochon from side to side, they are nearly colorless.
Synthetic corundum and spinel with fine lines engraved on the back in a three-sided pattern from which reflections to the top of the cabochon produce a star may be detected easily by inspection for the obvious line of demarcation between the top and back portions.
Synthetic star material made by Linde Air Products Co. is much more difficult to detect. To the eye, the color of these synthetic stars is so near the finest quality natural stone and the stars so perfect that the observer becomes suspicious that they are "too good to be true". However, for positive identification, the usual tests for synthetic corundum must be made. These tests will be described later in the course.
The milky chalcedony and other types of milky quartz that are often sold unethically as "moonstone" lack the floating, billowy, bluish or white light and the transparency of fine moonstone of the feldspar family. Some glass imitations of opal appear to be made by placing metal foil over a bead of glass near the melting point, then superimposing a second globule of glass with sufficient force to deform the foil so that it gives an impression vaguely akin to that of opal.
It is interesting that many jewelers who say that "colored stones don't sell" are likely to include in their stocks opals, star sapphires and cat's-eyes, because they have a certain amount of appreciation for these phenomenal stones and this appreciation enables them to sell such stones. Perhaps the reason for this is the tangibility of the unusual optical effects shown by these stones. The fact that no two fine opals, cat's -eyes, stars, alexandrites or other phenomenal gemstones are exactly alike, plus the unusual appearance that each displays, may be used most effectively by the jeweler who is appreciative of this distinctive beauty. In each man there seems to be opposing tendencies; on the one hand, not to be considered "different"; on the other, to be better in at least one respect than anyone else. The effective retailer of colored stones takes advantage of the latter tendency by appealing to the desire to own finer and more unusual things than any one else. This is a simple matter with phenomenal stones, each one of which may be presented to the prospective buyer as a stone that cannot be duplicated exactly. The most effective salesman of phenomenal gemstones that we have encountered surprised us with the statement that he could not sell diamonds. His deep appreciation for the unusual qualities represented by phenomenal stones made him so uniquely effective in their presentation to customers that by comparison, his sales of diamonds were low.
If you wish to be an accomplished salesman of phenomenal stones, take every opportunity to study their rare beauty. Visit every gem collection that you can.
Examine carefully the magnificent phenomenal gems not only in such collections, but in those that appear from time to time in traveler's stocks, jewelry-store windows, and elsewhere.
The recent growing popularity of star sapphires and the increased sales or natural star sapphires after the synthetic's introduction illustrates what can be accomplished if even a small amount of effort is put into familiarizing the public with phenomenal stones. The basis of effective selling is knowledge and appreciation. Knowledge of phenomenal stones builds your appreciation of them.