Pirotechnia by Vannoccio Biringuccio

But, with all this, I do not want to miss telling you a few things about goldsmithing (which are kept from ordinary people almost as secrets) so that you may know these as well. First the method of softening gold when it can no longer withstand the hammer blows because of some trace of lead or something else that it might have picked up. It is melted in a crucible and sprinkled over with crushed glass or a bit of sal alkali with wax, or three or four pinches of crushed sublimate and afterwards heated well. If the piece still lacks its yellow color, this can be restored by smearing it with verdigris and sal ammoniac tempered with urine or vinegar. It is heated over charcoal, and as soon as it is really how it is thrown into urine to scale it. It is also washed by boiling it in water with crushed yellow sulphur; such a method is used more with gilded silver than with gold pieces. Another way to restore the yellow color consists in boiling the piece in parings, or shall I say, filings of bull's or ram's horns or chopped straw or with the smoke of feathers or of the above-mentioned horns. But these devices are very short-lived. Similarly, when the silver is crude and coarse, it is softened with mercury mixed with leached wood ashes or by melting it with saltpeter, tartar, crushed glass or sal alkali and many other things concocted and discovered by alchemists. Silver is scaled and blanched by boiling it with tartar and common salt, and if you choose to do so, with a considerable amount of rock alum.

Soldering is also essential to this art because it is used quite often and requires great care. First it must be ascertained that the soldier is not harder than the piece to be soldered let the work, when heated, melt before the solder. It is necessary then to make the solder soft by corrupting it, lowering the carat or alloys through the addition of silver, brass or copper. Fine silver and fine gold, however, brought together with a little borax or verdigris can be joined with no extra solder. To solder, a special little furnace is needed, or else a chamber of coals, in the guise of a small furnace, can be arranged on the forge. The solder consists of fine silver, half brass, one-fourth of burned copper; it is broken up, cut in small pieces, mixed with a little borax and placed where it is supposed to flow on the object. This is bound, picked up with tongs and set over red-hot charcoal. By pumping quite a lot of air with a little bellows the fire is increased until the solder is seen flowing all along the seam. The pieces is then immediately removed and let cool. In this way each work broken or made in pieces is soldered well into one.

Works are also ornamented with nielloed intaglios and grooves. Niello consists of one part of fine silver, two parts of copper, three of pure lead. An earthenware flask with a long and narrow neck is filled half-way with ground sulphur over which the above-mentioned molten metals are poured. The flask opening is immediately sealed with earth and the flask is shaken well. When cold, the flask is broken, the metals are taken out, then cleaned, washed and finally ground. They are used for filling in the hollows in the objects as desired. Blowing with little bellows over a certain amount of wood flames in a small furnace made of large chunks of coal, the metal mixture is enlivened and made to run thoroughly by prodding and pressing it [into the hollows T.N.] with a little stick of wood or iron rod. When the niello has run, the piece is removed from the fire and let cool. Then the excess is filed off, the niello is polished with a reed and fine pumice and brought to a beautiful luster by rubbing it with tripoli.

Enameling is also part of this art. But few from this region are skilled in it because they are dependent on the enamels and the piece they want to enamel. In fact, each sort of gold and silver or copper requires enamels suited to its nature, otherwise it does not respond. In our region, craftsmen do not know how to prepare enamels so buy them ready-made. If they chance upon good ones, the work turns out good. If not, these local craftsmen, to avoid difficulties, make do with whatever is available to them. Now enamels are prepared first by grinding them fine and washing them several times. Each different color is kept separate in a little clean glazed bowl with a good amount of water free from impurities. Then some of the desired colors are picked up with a copper or iron style somewhat flattened at its point and spread over the work sort of thickly, filling all depressions. The water is then blotted out by pressing with some cotton or absorbent paper. The work, with all its parts to be enameled, covered and prepared in such manner, is placed over a charcoal fire in a clay furnace made for this purpose and equipped with a little muffler similar to those for assaying, or in a stove made of big chunks of coals as for soldering or niello. Blowing with little bellows a bran fire is kept going until the enamel is well fused. The excess is removed with a grinding wheel and, if the work is flat, it is evened out. Then the enamel is returned to the fire to vitrify it and bring out its luster again so as to reveal the beauty and charm of each color as it was set in its proper place.

Essential to this art is also a kind of work called filigree, which is actually achieved with gold or silver wires and by attaching spraywork, fruit or seeds or similar things on thick foil. First the wires are drawn through the drawplate to make the stems. Then the leaves are stamped over a piece of lead. The seeds, made of the same wire, are cut, chopped and melted in a crucible with a layer of ashes and removed when cold. These things are selected and arranged according to the design and attached to their proper place with a paste made of quince seeds or gum arabic. Finally the work is placed over one of the previously described furnaces with borax and soft gold or silver solder. The solder is made to flow with a fire of bran or dry alder twigs. Undoubtedly, whoever works in this appliqué technique and is skilled in it easily achieves beautiful results and such that they bewilder anybody who sees them.

Aside from the manual work the [goldsmith's T.N.] art has much in common with alchemy because so often it makes appear what is not there, as is evident in gem setting, in enhancing the color of gold, in blanching silver and also in gilding things which by true nature are silver, brass or copper and appear to be of gold. Moreover, things are made to look as if of gold and fine silver when they are not. To reach such an effect two ways are followed: one using hammered gold leaf layed over a piece previously activated with quicksilver, the other combining fine gold with mercury and spreading it with a copper rod over the piece. The mercury applied over the work by either method, is made to evaporate through heat leaving the gold. If the piece is gold, it is quenched in urine. If it is silver on copper or brass, it is thrown into oil and heated with a bran fire.

Each piece of gold or silver, as well as copper, is worked cold or hot, provided discretion is used in annealing the piece after each hammering or when necessary.

I think I have told you enough about the general procedure with gold or silver. Whatever else is necessary depends entirely on talent and practice.

But a most ingenious and beautiful thing, which should certainly not go unmentioned, is the discovery of making the foils that are placed under gems to enhance their beauty by revealing their peculiarity of brilliance and color. This composition was discovered through the observation of the tempering process, but it also employs the virtue of high heat and various fumes used for this purpose, in addition to the basic mixture and composition of the material.

Notes

1. Remark from MIT Press 1942 English translation of the Biringuccio text, made by Cyril Stanley Smith and Martha Teach Gnudi.
2. Purifying gold: in the Italian text cimentare, to purify or assay gold by means of a mixture called cimento, or to test gold with a touchstone.
3. To scale it: removing the build-up of silver from the surface revealing a richer gold underlay.
4. "These foils were necessitated by the old methods of cutting stones which did not cause total internal reflection of the incident light. They were made of various alloys of gold, silver and copper, hammered very thin, carefully cleaned and heated to develop temper colors. Cellini (Trattati della oreficeria e della scultura) describes their production in detail and lists the best alloys for each color." The Pyrotechnia of Vannoccio Biringuccio, the MIT Press, translated by Cyril Stanley Smith and Martha Teach Gnudi, 1942.

Vittoria Cozzi-Olivetti is an Italian metalsmith and translator living in California.