Ruskin advises us to "seek out and cast aside all
manner of false or dyed or altered stones" but, in spite of his advice,
perhaps the most justifiable use of heat treatment is that which alters
the color of true topaz from a wine-yellow to a fine pink. It would
appear that the wine-yellow is a composite color composed of pink and
yellow and that the pink constituent is less easily changed by heat than
is the yellow one. If too high a temperature is used both colors
disappear and white topaz results. As the latter is abundant in nature
and of little value, such a result is very undesirable. Pink topaz,
however, is very rare, and until recently, when pink tourmaline from
California and Madagascar, and pink beryl (morganite) from Madagascar,
became available in quantity, the "pinked" topazes had but few competing
gems, and thus commanded a higher price than the natural topazes. Of
course, care has to be taken in heating a mineral to raise and lower the
temperature slowly, in order to avoid sudden and unequal expansion or
contraction, which would crack and ruin the specimen, as the writer
learned to his sorrow with the first topaz that he tried to "pink."

SPANISH TOPAZ. Another material that gains a more valuable color by heat
treatment is the smoky quartz of Spain, which, on being gently heated,
yields the so-called Spanish topaz. Some amethysts are altered to a
yellow color by mild heating. Too great a temperature completely
decolorizes colored quartz. Some dark quartz yields a nearly garnet red
product, after heating.

ZIRCON. Slight increase in temperature causes many of the zircons from
Ceylon to change markedly in color. An alcohol flame serves admirably to
effect the change, care being taken to warm up the stone very gradually
and to cool it slowly. Drafts should be prevented, as they might
suddenly cool the stone and crack it. Some zircons become completely
whitened by this treatment. At the same time they increase markedly in
density and in refractive index and thus become even more snappy and
brilliant than when colored. One is tempted to suspect that the "space
lattice" of the crystal has had its strata drawn closer together during
the heating and left permanently in a closer order of arrangement. Other
zircons merely become lighter colored and less attractive. Some of the
whitened stones again become more or less colored on exposure to strong
light. Ultra-violet light will sometimes restore these to a fine dee