The method of using copper minerals for soldering gold in ancient times has evidently puzzled many modern writers on early technical arts, though the correct explanation was given at the end of the eighteenth century by Guettard, who showed experimentally that malachite, for example, could be used as a solder for gold.138 All that is required is that some suitable reducing agent, such as charcoal or organic matter, should be present, and that the temperature should be high enough to reduce the mineral to copper and to make this melt and alloy with the gold. It has recently been shown for the first time that certain types of ancient goldwork could only have been produced by a soldering process of this sort. Some Etruscan and Greek works of art contain delicate patterns formed by minute grains of gold or very fine wire joined to a background of solid metal; it has been found by experiment that they could not have been joined together by the direct application of solder in the form of molten metal or by any process of fusion welding. Furthermore, microscopic examination of examples of ancient goldwork has shown the use of this reduction metiiod of soldering.189
It is interesting to note that this ancient method of soldering gold by the reduction of a copper compound in situ is the subject of a modern patent140 issued to a Mr. Littledale, who may be regarded as the rediscoverer of an old method of soldering which is used for goldwork of great delicacy.
The name chrysocolla was applied by writers later than Theophrastus to artificial copper preparations used for soldering gold. Pliny141 describes a mixture of this sort. In addition, he mentions under chrysocolla a preparation that contained gold and silver in addition to copper salts. By further extension of the original meaning, the name was applied to alloys used for the soldering of gold. In the Leyden Papyrus X are two recipes (Nos. 31 and 33) for the preparation of such gold solders.142 In Number 31, the alloy of copper, silver, and gold is called το χρνσόκολλον.
138 Bailey, The Elder Pliny's Chapters on Chemical Subjects, Part I, p. 206.
139 H. Maryon, Technical Studies in the Field of the Fine Arts, V (1936), 88-95.
140 British patent, 1934, No. 415181.
141 XXXIII, 93.
142 M. Berthelot, Archeologie et Histoire des Sciences (Paris, 1906), pp. 280, 282.
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