When the cakes have been thus arranged through the hole at the top of the dome, he throws in charcoal with a basket woven of wooden twigs. Then he places the lid over the dome, and the assistant covers over the joints with lute. The master himself throws half a basketful of charcoal into the crucible through the aperture next to the nozzle pipe, and prepares the bellows, in order to be able to begin the second operation on the morning of the following day. It takes the space of one hour to carry out such a piece of work, and at twelve all is prepared. These hours all reckoned up make a sum of eight hours.
Now it is time that we should come to the second operation. In the morning the workman takes up two shovelsful of live charcoals and throws them into the crucible through the aperture next to the pipes of the nozzles; then through the same hole he lays upon them small pieces of fir-wood or of pitch pine, such as are generally used to cook fish. After this the water-gates are opened, in order that the machine may be turned which depresses the levers of the bellows. In the space of one hour the lead alloy is melted; and when this has been done, he places four sticks of wood, twelve feet long, through the hole in the back of the dome, and as many through the channel; these sticks, lest they should damage the crucible, are both weighted on the ends and supported by trestles; these trestles are made of a beam, three feet long, two palms and as many digits wide, two palms thick, and have two spreading legs at each end. Against the trestle, in front of the channel, there is placed an iron plate, lest the litharge, when it is extracted from the furnace, should splash the smelter's shoes and injure his feet and legs. With an iron shovel or a fork he places the remainder of the cakes through the aperture at the back of the dome on to the sticks of wood already mentioned.
The native silver, or silver glance, or grey silver, or ruby silver, or any other sort, when it has been flattened out[32], and cut up, and heated in an iron crucible, is poured into the molten lead mixed with silver, in order that impurities may be separated. As I have often said, this molten lead mixed with silver is called stannum[33].
If it be difficult to separate the lead from the silver, he throws copper and charcoal dust into the molten silver-lead alloy. If the alloy of argentiferous gold and lead, or the silver-lead alloy, contains impurities from the ore, then he throws in either equal portions of argol and Venetian glass or of sal-ammoniac, or of Venetian glass and of Venetian soap; or else unequal portions, that is, two of argol and one of iron rust; there are some who mix a little saltpetre with each compound. To one centumpondium of the alloy is added a bes or a libra and a third of the powder, according to whether it is more or less impure. The powder certainly separates the impurities from the alloy. Then, with a kind of rabble he draws out through the channel, mixed with charcoal, the scum, as one might say, of the lead; the lead makes this scum when it becomes hot, but that less of it may be made it must be stirred frequently with the bar.
Within the space of a quarter of an hour the crucible absorbs the lead; at the time when it penetrates into the crucible it leaps and bubbles. Then the master takes out a little lead with an iron ladle, which he assays, in order to find what proportion of silver there is in the whole of the alloy; the ladle is five digits wide, the iron part of its handle is three feet long and the wooden part the same. Afterward, when they are heated, he extracts with a bar the litharge which comes from the lead and the copper, if there be any of it in the alloy. Wherefore, it might more rightly be called spuma of lead than of silver[34]. There is no injury to the silver, when the lead and copper are separated from it. In truth the lead becomes much purer in the crucible of the other furnace, in which silver is refined. In ancient times, as the author Pliny[35] relates, there was under the channel of the crucible another crucible, and the litharge flowed down from the upper one into the lower one, out of which it was lifted up and rolled round with a stick in order that it might be of moderate weight. For which reason, they formerly made it into small tubes or pipes, but now, since it is not rolled round a stick, they make it into bars.
If there be any danger that the alloy might flow out with the litharge, the foreman keeps on hand a piece of lute, shaped like a cylinder and pointed at both ends; fastening this to a hooked bar he opposes it to the alloy so that it will not flow out.
