A description of gold and silver is necessarily accompanied by that of the stone known as “coticula.”[1037] In former times, according to Theophrastus, this stone was nowhere to be found, except in the river Tmolus,[1038] but at the present day it is found in numerous places. By some persons it is known as the “Heraclian,” and by others as the “Lydian” stone. It is found in pieces of moderate size, and never exceeding four inches in length by two in breadth. The side that has lain facing the sun is superior[1039] to that which has lain next to the ground. Persons of experience in these matters, when they have scraped a particle off the ore with this stone, as with a file, can tell in a moment the proportion of gold there is in it, how much silver, or how much copper; and this to a scruple, their accuracy being so marvellous that they are never mistaken.
CHAP. 44.—THE DIFFERENT KINDS OF SILVER, AND THE MODES OF TESTING IT.
There are two kinds of silver. On placing a piece of it upon an iron fire-shovel at a white heat, if the metal remains perfectly white, it is of the best quality: if again it turns of a reddish colour, it is inferior; but if it becomes black, it is worthless. Fraud, however, has devised means of stultifying this test even; for by keeping the shovel immersed in men’s urine, the piece of silver absorbs it as it burns, and so displays a fictitious whiteness. There is also a kind of test with reference to polished silver: when the human breath comes in contact with it, it should immediately be covered with steam,[1040] the cloudiness disappearing at once.
CHAP. 45. (9.)—MIRRORS.
It is generally supposed among us that it is only the very finest silver that admits of being laminated, and so converted into mirrors. Pure silver was formerly used for the purpose, but, at the present day, this too has been corrupted by the devices of fraud. But, really, it is a very marvellous property that this metal has, of reflecting objects; a property which, it is generally agreed, results from the repercussion of the air,[1041] thrown back as it is from the metal upon the eyes. The same too is the action that takes place when we use a mirror. If, again, a thick plate of this metal is highly polished, and is rendered slightly concave,[1042] the image or object reflected is enlarged to an immense extent; so vast is the difference between a surface receiving,[1043] and throwing back the air. Even more than this—drinking-cups are now made in such a manner, as to be filled inside with numerous[1044] concave facets, like so many mirrors; so that if but one person looks into the interior, he sees reflected a whole multitude of persons.
Mirrors, too, have been invented to reflect monstrous[1045] forms; those, for instance, which have been consecrated in the Temple at Smyrna. This, however, all results from the configuration given to the metal; and it makes all the difference whether the surface has a concave form like the section of a drinking cup, or whether it is [convex] like a Thracian[1046] buckler; whether it is depressed in the middle or elevated; whether the surface has a direction[1047] transversely or obliquely; or whether it runs horizontally or vertically; the peculiar configuration of the surface which receives the shadows, causing them to undergo corresponding distortions: for, in fact, the image is nothing else but the shadow of the object collected upon the bright surface of the metal.
However, to finish our description of mirrors on the present[1048] occasion—the best, in the times of our ancestors, were those of Brundisium,[1049] composed of a mixture of[1050] stannum and copper: at a later period, however, those made of silver were preferred, Pasiteles[1051] being the first who made them, in the time[1052] of Pompeius Magnus. More recently,[1053] a notion has arisen that the object is reflected with greater distinctness, by the application to the back of the mirror of a layer of gold.[1054]
CHAP. 46.—EGYPTIAN SILVER.
The people of Egypt stain their silver vessels, that they may see represented in them their god Anubis;[1055] and it is the custom with them to paint,[1056] and not to chase, their silver. This usage has now passed to our own triumphal statues even; and, a truly marvellous fact, the value of silver has been enhanced by deadening its brilliancy.[1057] The following is the method adopted: with the silver are mixed two-thirds of the very finest Cyprian copper, that known as “coronarium,”[1058] and a proportion of live sulphur equal to that of the silver. The whole of these are then melted in an earthen vessel well luted with potter’s clay, the operation being completed when the cover becomes detached from the vessel. Silver admits also of being blackened with the yolk of a hard-boiled egg; a tint, however, which is removed by the application of vinegar and chalk.