George W. Fischer
Articles and Videos by George W. Fischer:
The prime requisite for coloration of gemstone is that it be porous . That is to say there must be spaces or vacancies into which the coloring chemical, in solution, can penetrate deeply in order to impart the desired color. These spaces are usually spoken of as “pores”, but from what I have been able to observe, they are not pores in the sense of parallel tubes. Rather, they are.
There are several reactions well known to chemists, involving iron compounds and prussiate compounds (ferrocyanides and ferricyanides) that yield characteristic blue precipitates. All are applicable to chemical coloration of gemstone, but since they do not differ significantly for our purposes, only one is included in this book. It involves a reaction between potassium ferricyanide and ferrous sulfate, producing a blue precipitate known as “Turnbulls Blue”.
The use of cobalt compounds to impart blue hues to glass, glazes and enamels has been known for centuries. “Cobalt blue” glass is familiar to just about everyone. It seemed logical that cobalt compounds could be useful to impart color to gemstone and this has proven to be true. Several cobalt processes follow.
Various and attractive shades of blue can be induced in gemstone by the use of copper compounds. This is perfectly logical, considering that several of our blue gemstone or mineral species owe their color to the presence of copper compounds. Familiar examples of these are malachite, chrysocolla, turquoise and azurite.
The most important detail in the preparation of gemstone for chemical coloration is that it be clean. Oil and grease, especially, must be entirely removed. I have found it practical to keep a bucket of detergent solution (ordinarily laundry detergent) standing beside the slab saw. Two or three cups full of detergent powder in about four gallons of water (in a five gallon bucket) is adequate. As the slabs come from the saw, they are dropped carefully into the bucket and allowed to accumulate there.
There are only two ways that I know of to induce black into gemstone. One of these involves carbon while the other is silver. Theoretically, there should be several other methods possible. I have tested these out however, and they have proved impractical. But black is black, so multiple means of inducing it are not needed. The two presented here are different in that one, the silver, is black with a metallic sheen or luster.
There are only a few inorganic processes, in my experience at least, that will impart pinks or reds to gemstone. These involve primarily four metals – cobalt, iron, mercury and silver. We already know cobalt can induce blue, purple, amethyst, etc. and incidentally pink in gemstone. There are also two additional cobalt processes that impart pink or lavender, primarily or exclusively. Several iron compounds are red or reddish, common rust being a familiar example and at least one of these is useful in coloring gemstone. The same is true of mercury. And there are two red-silver compounds that are adaptable to coloring gemstone.
At first consideration, it might seem poor organization to include browns and yellows in the same chapter. However, I do this because in some instances the same process imparts brown hues to some gemstone varieties and yellow to others. Admittedly, brown may not be a favorite gemstone color in nature among rockhounds and lapidaries, but the browns imparted by some of these processes to at least some of the gemstone varieties I have been using are attractive in cabochons made from them.
It seems that everyone likes the greens in chemically colored gemstone. Probably this is because greens are almost universally pleasing to the eye. No doubt this accounts for the great popularity of naturally green gemstone such as jade, chrysoprase, emerald, malachite, etc. Fortunately, there are several processes that will impart green hues to some gemstone varieties. Some of these are bluish-green and are included here rather than among The Blues…
This book is the culmination of some twenty-five years of personally supported research on the use of inorganic chemicals to induce color and inclusions in gemstone. Prior attempts to use dyes for gemstone colorations had proved very disappointing. The fact that native color in gemstone is derived from the presence of compounds of certain metals as inorganic components (impurities) of the gemstone suggested that the inorganic salts of these metals might serve well to induce color where color is lacking or needs enhancing.
Since the discovery that the principle of electrochemical displacement of metals can be used effectively and easily to induce inclusions in snakeskin agate, I have tried the method on several of the other gemstone varieties and have found that some respond with interesting and pleasing results. These are coconut agate, Brazil carnelian and troyite. Besides these, several other agates have responded well to the process.
Dendrites, moss, plume and similar inclusions have added interest
and value to gemstone for about as long as man has been aware of the
beauty and gem potential of such “rock”. But apparently up to now,
man has been dependent on inclusions formed in nature. The process
by which they developed in nature has been only vaguely understood
and thought to require long periods of time, even in the geological
concept of time. Any means, therefore, of inducing the formation of
inclusions in gemstone is automatically of more than transitory
Tin inclusions can be induced in agate and other gemstone varieties in much the same way as with copper. Just as copper inclusions are made from copper chloride, so tin inclusions are made from tin chloride. Copper chloride imparts green and finally blue-green color to the agates, but tin chloride is colorless unless it happens to have some native color of its own. Furthermore, agate with induced tin inclusions does not lend itself to complementary color variations like the copper included agate does. It seems that, with few exceptions, slabs that have been impregnated with tin chloride will not absorb additional chemicals in solution.