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The Burning and Colouring of Precious Stones. 49
stones. The use of honey in the dyeing of stones was in early times the secret of a few Agate merchants at Idar, who obtained it from some Romans who periodically came to procure various kinds of Onyx from the stone-polishers at that place and at Oberstein. It is impossible to say whether these Romans acquired the knowledge by reading Pliny, or received it as a tradition in Italy.
The Art is based on the fact that the alternate layers of the Chalcedony, in the agate nodule are not equally porous, some strata readily absorbing a colouring liquid, while others imbibe little or none of it. The porosity of certain layers led the stone-polishers to conclude that they might so colour these as to render mean and insignificant-looking stones suitable for Cameos and cognate purposes, and thereby materially increase their value.
The Agate merchants before purchasing a stone, test the worth of the raw stone for dyeing by striking a thin piece off it, damping it with the tongue, and observing whether the drying of the stripes takes place quickly or slowly. If the stripes absorb the moisture readily, the stone is good for dyeing, and especially for Onyx-dyeing. This test, however, cannot always be relied on, and the manipulators are sometimes obliged to colour a small piece experimentally before buying the stones.
At Oberstein and Idar the Onyx is dyed in the
following manner. The stone is twice washed, and then
dried. It is next laid in honey and water (half-a-pound
of honey to about sixteen or twenty ounces of water) or
in sugar and water, or in oil. The dish in which it is
laid must be clean. This is placed in a warm oven or
on a stove, and care must be taken that the stone is
always covered with the liquid, and that the liquid does
not boil. This treatment is continued for a period of
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