A History of Inventions, Discoveries, and Origins, Volume II (of 2). Johann Beckmann

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СКАЧАТЬ of the age, that every young woman in their time must have a silver mirror. These polished silver plates may however have been very slight, for all the ancient mirrors, preserved in collections, which I have ever seen, are only covered with a thin coat of that expensive metal; and in the like manner our artists have at length learned a method of making the cases of gold and silver watches so thin and light, that every footman and soldier can wear one. At first the finest silver only was employed for these mirrors, because it was imagined that they could not be made of that which was standard; but afterwards metal was used of an inferior quality. Pliny tells us so expressly, and I form the same conclusion from a passage of Plautus150. Philematium having taken up a mirror, the prudent Scapha gives her a towel, and desires her to wipe her fingers, lest her lover should suspect by the smell that she had been receiving money. Fine silver however communicates as little smell to the fingers as gold; but it is to be remembered that the ancients understood much better than the moderns how to discover the fineness of the noble metals by the smell, as many modes of proof which we use to find out the alloy, were to them unknown. Money-changers therefore employed their smell when they were desirous of trying the purity of coin151. The witty thought of Vespasian, who, when reproached on account of his tax upon urine, desired those who did so to smell the money it produced, and to tell him whether it had any smell of the article which was the object of it, alludes to this circumstance. In the like manner many savage nations at present can by their smell determine the purity of gold152.

      We are informed by Pliny, that Praxiteles, in the time of Pompey the Great, made the first silver mirror, and that mirrors of that metal were preferred to all others. Silver mirrors however were known long before that period, as is proved by the passage of Plautus above-quoted. To reconcile this contradiction, Meursius remarks that Pliny speaks only of his countrymen, and not of the Greeks, who had such articles much earlier, and the scene in Plautus is at Athens. This therefore seems to justify the account of Pliny, but of what he says afterwards I can find no explanation. Hardouin is of opinion, that mirrors, according to the newest invention, at that period, were covered behind with a plate of gold, as our mirrors are with an amalgam. But as the ancient plates of silver were not transparent, how could the gold at the back part of them produce any effect in regard to the image? May not the meaning be, that a thin plate of gold was placed at some distance before the mirror in order to throw more light upon its surface? But whatever may have been the case, Pliny himself seems not to have had much confidence in the invention.

      Mirrors of copper, brass and gold, I have found mentioned only by the poets, who perhaps employed the names of these metals because they best suited their measure, or because they wished to use uncommon expressions, and thought a golden mirror the noblest. By the brass ones perhaps are to be understood only such as were made of mixed copper. Did golden mirrors occur oftener, I should be inclined to refer the epithet rather to the frame or ornaments than to the mirror itself; for at present we say a gold watch, though the cases only may be of that metal.

      Mirrors seem for a long time to have been made of a mixture of copper and tin, as is expressly said by Pliny153, who adds, that the best were constructed at Brundisium. This mixture, which was known to Aristotle, produces a white metal, which, on account of its colour, may have been extremely proper for the purpose, and even at present the same mixture, according to the careful experiments made by Mr. Mudge, an Englishman154, produces the best metal for specula. It appears that the ancients had not determined the proportion very accurately; for Pliny assures us twice that in his time mirrors of silver were preferred. It is indeed not easy to ascertain the quantity of each metal that ought to be taken, and the most advantageous degree of heat; upon which a great deal depends. One of the principal difficulties is to cast the metal without blisters or air-holes, and without causing any part of the tin to oxidize, which occasions knots and cracks, and prevents it from receiving a fine polish. A passage of Lucian155, which no one as yet has been able to clear up, alludes certainly, in my opinion, to these faults. A mixture of copper and tin is so brittle, that it is very liable to crack; and a mirror formed of it, if not preserved with great care, soon becomes so dim, that it cannot be used till it has been previously cleaned and polished. For this reason a sponge with pounded pumice-stone was generally suspended, from the ancient mirrors, and they were kept likewise in a case or box, as may be seen by the greater part of those still extant. Mirrors of silver were less subject to this inconvenience, and I am inclined to think that the latter on this account made the former be disused, as we are informed by Pliny.

      As ancient mirrors of metal are still to be found in collections of antiquities, it might be of some importance to the arts if chemical experiments were made on their composition. Those who have hitherto given us any account of them have contented themselves with describing their external figure and shape. Count Caylus156 is the only person, as far as I know, who caused any chemical experiments to be undertaken on this subject. They were made on a mirror found near Naples, by M. Roux, who asserts that the composition was a mixture of copper and regulus of antimony, with a little lead. Antimony however was not known to the ancients. If that metal was really a component part, the mirror must have been the work of more modern times, or it must be allowed that the artist had metal combined with antimony without knowing it; but the latter is not probable. The experiments made by Roux do not seem to me to have proved in a satisfactory manner the presence of regulus of antimony; moreover, no certain information can be derived from them, for the antiquity of the mirror was not ascertained; nor was it known whether it ought to be reckoned amongst the best or the worst of the period when it was made.

      Those mirrors, which were so large that one could see one’s self in them at full length, must, in all probability, have consisted of polished plates of silver; for to cast plates of such a size of copper and tin would have required more art than we can allow to those periods; and I do not know whether our artists even now would succeed in them157.

      We read in various authors, that, besides metals, the ancients formed stones into mirrors, which were likewise in use. It is undoubtedly certain that many stones, particularly of the vitreous kind, which are opake and of a dark colour, would answer exceedingly well for that purpose; but let the choice have been ever so good, they would not, in this respect, have been nearly equal to metals. These of all mineral bodies have the most perfect opacity; and for that reason the greatest lustre: both these properties are produced by their solidity; and hence they reflect more perfectly, and with more regularity, the rays of light that proceed from other bodies. Our glass mirrors, indeed, are properly metallic. Stones, on the other hand, have at any rate some, though often hardly perceptible, transparency; so that many of the rays of light are absorbed, or at least not reflected. Mention of stone mirrors occurs also so seldom in the ancients, that we may conclude they were made rather for ornament than real utility. In general, we find accounts only of polished plates or panels of stone, fixed in the walls of wainscoted apartments, which were celebrated on account of their property of reflection.

      Pliny158 praises in this respect the obsidian stone, or, as it is now called, the Icelandic agate. Everything that he says of it will be perfectly intelligible to those who are acquainted with this species of stone or vitrified lava. The image reflected from a box made of it, which I have in my possession, is like a shadow or silhouette; but with this difference, that one sees not only the contour, but also the whole figure distinctly, though the colours are darkened. To form it into images and utensils, which Pliny speaks of, must have been exceedingly difficult, on account of its brittleness. I saw at Copenhagen, among other things made of it, a drinking-cup and cover, on which the artist had been employed four years.

      Domitian, when he suspected that plots were formed against him, caused a gallery, in which he used to walk, to be lined with phengites, which by its reflection showed everything that was done behind his backСКАЧАТЬ