White lead is naturally more dry; while the black, on the contrary, is always moist; consequently the white, without being mixed with another metal, is of no use[1717] for anything. Silver too, cannot be soldered with it, because the silver becomes fused before the white lead. It is confidently stated, also, that if too small a proportion of black lead is mixed with the white, this last will corrode the silver. It was in the Gallic provinces that the method was discovered of coating articles of copper with white lead, so as to be scarcely distinguishable from silver: articles thus plated are known as “incoctilia.”[1718] At a later period, the people of the town of Alesia[1719] began to use a similar process for plating articles with silver, more particularly ornaments for horses, beasts of burden, and yokes of oxen: the merit, however, of this invention belongs to the Bituriges.[1720] After this, they began to ornament their esseda, colisata, and petorita[1721] in a similar manner; and luxury has at last arrived at such a pitch, that not only are their decorations made of silver, but of gold even, and what was formerly a marvel to behold on a cup, is now subjected to the wear and tear of a carriage, and this in obedience to what they call fashion! White lead is tested, by pouring it, melted,[1722] upon paper, which ought to have the appearance of being torn rather by the weight than by the heat of the metal. India has neither copper nor lead,[1723] but she procures them in exchange for her precious stones and pearls. CHAP. 49.—BLACK LEAD. Black lead[1724] is used in the form of pipes and sheets: it is extracted with great labour in Spain, and throughout all the Gallic provinces; but in Britannia[1725] it is found in the upper stratum of the earth, in such abundance, that a law has been spontaneously made, prohibiting any one from working more than a certain quantity of it. The various kinds of black lead are known by the following names—the Ovetanian,[1726] the Caprariensian,[1727] and the Oleastrensian.[1728] There is no difference whatever in them, when the scoria has been carefully removed by calcination. It is a marvellous fact, that these mines, and these only, when they have been abandoned for some time, become replenished, and are more prolific than before. This would appear to be effected by the air, infusing itself at liberty through the open orifices, just as some women become more prolific after abortion. This was lately found to be the case with the Santarensian mine in Bætica;[1729] which, after being farmed at an annual rental of two hundred thousand denarii, and then abandoned, is now rented at two hundred and fifty-five thousand per annum. In the same manner, the Antonian mine in the same province has had the rent raised to four hundred thousand sesterces per annum.