We assay an alloy of copper and silver in the following way. From a few cakes of copper the assayer cuts out portions, small samples from small cakes, medium samples from medium cakes, and large samples from large cakes; the small ones are equal in size to half a hazel nut, the large ones do not exceed the size of half a chestnut, and those of medium size come between the two. He cuts out the samples from the middle of the bottom of each cake. He places the samples in a new, clean, triangular crucible and fixes to them pieces of paper upon which are written the weight of the cakes of copper, of whatever size they may be; for example, he writes, "These samples have been cut from copper which weighs twenty centumpondia." When he wishes to know how much silver one centumpondium of copper of this kind has in it, first of all he throws glowing coals into the iron hoop, then adds charcoal to it. When the fire has become hot, the paper is taken out of the crucible and put aside, he then sets that crucible on the fire and gradually heats it for a quarter of an hour until it becomes red hot. Then he stimulates the fire by blowing with a blast from the double bellows for half an hour, because copper which is devoid of lead requires this time to become hot and to melt; copper not devoid of lead melts quicker. When he has blown the bellows for about the space of time stated, he removes the glowing charcoal with the tongs, and stirs the copper with a splinter of wood, which he grasps with the tongs. If it does not stir easily, it is a sign that the copper is not wholly liquefied; if he finds this is the case, he again places a large piece of charcoal in the crucible, and replaces the glowing charcoal which had been removed, and again blows the bellows for a short time. When all the copper has melted he stops using the bellows, for if he were to continue to use them, the fire would consume part of the copper, and then that which remained would be richer than the cake from which it had been cut; this is no small mistake.
Others stir the molten copper with a stick of linden tree charcoal, and then pour it over a bundle of new clean birch twigs, beneath which is placed a wooden tub of sufficient size and full of water, and in this manner the copper is broken up into little granules as small as hemp seeds. Others employ straw in place of twigs. Others place a broad stone in a tub and pour in enough water to cover the stone, then they run out the molten copper from the crucible on to the stone, from which the minute granules roll off; others pour the molten copper into water and stir it until it is resolved into granules. The fire does not easily melt the copper in the cupel unless it has been poured and a thin leaf made of it, or unless it has been resolved into granules or made into filings; and if it does not melt, all the labour has been undertaken in vain. In order that they may be accurately weighed out, silver and lead are resolved into granules in the same manner as copper. But to return to the assay of copper. When the copper has been prepared by these methods, if it is free of lead and iron, and rich in silver, to each centumpondium (lesser weights) add one and a half unciae of lead (larger weights). If, however, the copper contains some lead, add one uncia of lead; if it contains iron, add two unciae. First put the lead into a cupel, and after it begins to smoke, add the copper; the fire generally consumes the copper, together with the lead, in about one hour and a quarter. When this is done, the silver will be found in the bottom of the cupel. The fire consumes both of those metals more quickly if they are heated in that furnace which draws in air. It is better to cover the upper half of it with a lid, and not only to put on the muffle door, but also to close the window of the muffle door with a piece of charcoal, or with a piece of brick. If the copper be such that the silver can only be separated from it with difficulty, then before it is tested with fire in the cupel, lead should first be put into the scorifier, and then the copper should be added with a moderate quantity of melted salt, both that the lead may absorb the copper and that the copper may be cleansed of the dross which abounds in it.
Tin which contains silver should not at the beginning of the assay be placed in a cupel, lest the silver, as often happens, be consumed and converted into fumes, together with the tin. As soon as the lead[35] has begun to fume in the scorifier, then add that[36] to it. In this way the lead will take the silver and the tin will boil and turn into ashes, which may be removed with a wooden splinter. The same thing occurs if any alloy is melted in which there is tin. When the lead has absorbed the silver which was in the tin, then, and not till then, it is heated in the cupel. First place the lead with which the silver is mixed, in an iron pan, and stand it on a hot furnace and let it melt; afterward pour this lead into a small iron mould, and then beat it out with a hammer on an anvil and make it into leaves in the same way as the copper. Lastly, place it in the cupel, which assay can be carried out in the space of half an hour. A great heat is harmful to it, for which reason there is no necessity either to cover the half of the furnace with a lid or to close up its mouth.
The minted metal alloys, which are known as money, are assayed in the following way. The smaller silver coins which have been picked out from the bottom and top and sides of a heap are first carefully cleansed; then, after they have been melted in the triangular crucible, they are either resolved into granules, or made into thin leaves. As for the large coins which weigh a drachma, a sicilicus, half an uncia, or an uncia, beat them into leaves. Then take a bes of the granules, or an equal weight of the leaves, and likewise take another bes in the same way. Wrap each sample separately in paper, and afterwards place two small pieces of lead in two cupels which have first been heated. The more precious the money is, the smaller portion of lead do we require for the assay, the more base, the larger is the portion required; for if a bes of silver is said to contain only half an uncia or one uncia of copper, we add to the bes of granules half an uncia of lead. If it is composed of equal parts of silver and copper, we add an uncia of lead, but if in a bes of copper there is only half an uncia or one uncia of silver, we add an uncia and a half of lead. As soon as the lead has begun to fume, put into each cupel one of the papers in which is wrapped the sample of silver alloyed with copper, and close the mouth of the muffle with charcoal. Heat them with a gentle fire until all the lead and copper are consumed, for a hot fire by its heat forces the silver, combined with a certain portion of lead, into the cupel, in which way the assay is rendered erroneous. Then take the beads out of the cupel and clean them of dross. If neither depresses the pan of the balance in which it is placed, but their weight is equal, the assay has been free from error; but if one bead depresses its pan, then there is an error, for which reason the assay must be repeated. If the bes of coin contains but seven unciae of pure silver it is because the King, or Prince, or the State who coins the money, has taken one uncia, which he keeps partly for profit and partly for the expense of coining, he having added copper to the silver. Of all these matters I have written extensively in my book De Precio Metallorum et Monetis.
We assay gold coins in various ways. If there is copper mixed with the gold, we melt them by fire in the same way as silver coins; if there is silver mixed with the gold, they are separated by the strongest aqua valens; if there is copper and silver mixed with the gold, then in the first place, after the addition of lead, they are heated in the cupel until the fire consumes the copper and the lead, and afterward the gold is parted from the silver.
It remains to speak of the touchstone[37] with which gold and silver are tested, and which was also used by the Ancients. For although the assay made by fire is more certain, still, since we often have no furnace, nor muffle, nor crucibles, or some delay must be occasioned in using them, we can always rub gold or silver on the touchstone, which we can have in readiness. Further, when gold coins are assayed in the fire, of what use are they afterward? A touchstone must be selected which is thoroughly black and free of sulphur, for the blacker it is and the more devoid of sulphur, the better it generally is; I have written elsewhere of its nature[38]. First the gold is rubbed on the touchstone, whether it contains silver or whether it is obtained from the mines or from the smelting; silver also is rubbed in the same way. Then one of the needles, that we judge by its colour to be of similar composition, is rubbed on the touchstone; if this proves too pale, another needle which has a stronger colour is rubbed on the touchstone; and if this proves too deep in colour, a third which has a little paler colour is used. For this will show us how great a proportion of silver or copper, or silver and copper together, is in the gold, or else how great a proportion of copper is in silver.
These needles are of four kinds.[39] The first kind are made of gold and silver, the second of gold and copper, the third of gold, silver, and copper, and the fourth of silver and copper. The first three kinds of needles are used principally for testing gold, and the fourth for silver. Needles of this kind are prepared in the following ways. The lesser weights correspond proportionately to the larger weights, and both of them are used, not only by mining people, but by coiners also. The needles are made in accordance with the lesser weights, and each set corresponds to a bes, which, in our own vocabulary, is called a mark. The bes, which is employed by those who coin gold, is divided into twenty-four double sextulae, which are now called after the Greek name ceratia; and each double sextula is divided into four semi-sextulae, which are called granas; and each semi-sextula is divided into three units of four siliquae each, of which each unit is called a grenlin. If we made the needles to be each four siliquae, there would be two hundred and eighty-eight in a bes, but if each were made to be a semi-sextula or a double scripula, then there would be ninety-six in a bes. By these two methods too many needles would be made, and the majority of them, by reason of the small difference in the proportion of the gold, would indicate nothing, therefore it is advisable to make them each of a double sextula; in this way twenty-four needles are made, of which the first is made of twenty-three duellae of silver and one of gold. Fannius is our authority that the Ancients called the double sextula a duella. When a bar of silver is rubbed on the touchstone and colours it just as this needle does, it contains one duella of gold. In this manner we determine by the other needles what proportion of gold there is, or when the gold exceeds the silver in weight, what proportion of silver.
