Gaul more particularly, where the ore is melted between red-hot stones, that the difference is to be seen that is produced by these variations in the method of smelting. Indeed, this last method scorches the metal, and renders it black and friable. Besides, they only melt it twice; whereas, the oftener this operation is repeated, the better in quality it becomes. (9.) It is also as well to remark that all copper fuses best when the weather is intensely cold. The proper combination for making statues and tablets is as follows: the ore is first melted; after which there is added to the molten metal one third part of second-hand[1591] copper, or in other words, copper that has been in use and bought up for the purpose. For it is a peculiarity of this metal that when it has been some time in use, and has been subject to long-continued friction, it becomes seasoned, and subdued, as it were, to a high polish. Twelve pounds and a half of silver-lead are then added to every hundred pounds of the fused metal. There is also a combination of copper, of a most delicate nature, “mould-copper,”[1592] as it is called; there being added to the metal one tenth part of lead[1593] and one twentieth of silver-lead, this combination being the best adapted for taking the colour known as “Græcænicus.”[1594] The last kind is that known as “ollaria,”[1595] from the vessels that are made of it: in this combination three or four pounds of silver-lead[1596] are added to every hundred pounds of copper. By the addition of lead to Cyprian copper, the purple tint is produced that we see upon the drapery of statues. CHAP. 21.—THE METHOD OF PRESERVING COPPER. Copper becomes covered with verdigris more quickly when cleaned than when neglected, unless it is well rubbed with oil. It is said that the best method of preserving it is with a coating of tar. The custom of making use of copper for monuments, which are intended to be perpetuated, is of very ancient date: it is upon tablets of brass that our public enactments are engraved. CHAP. 22. (10.)—CADMIA.