It is in the thirteenth century, that I find the first undoubted mention of glass mirrors covered at the back with tin or lead. Johannes Peckham, or Peccam, an English Franciscan monk, who taught at Oxford, Paris, and Rome, and who died in 1292, wrote about the year 1279 a treatise of optics, which was once printed, with the title of Johannis Pisani Perspectiva Communis191. In this work, besides mirrors made of iron, steel, and polished marble, the author not only speaks often of glass mirrors, but says also that they were covered on the back with lead, and that no image was reflected when the lead was scraped off. Vincentius Bellovacensis192 speaks in a manner still clearer, for he tells us that lead was poured over the glass plate while hot. To the same century also belong the concurrent testimonies of Raimundus Lullius193, Roger Bacon194, Antonius di Padua195, and Nicephorus Gregoras196, who died after the year 1360197.
That this invention cannot be much older we have reason to conclude, because glass mirrors were extremely scarce in France even in the fourteenth century, while mirrors of metal were in common use; and we are told that the mirror of Anne de Bretagne, consort of Louis XII., was of the latter kind198. Metal mirrors also were made and employed in Persia and the East, where indeed ancient usages continued longest, and glass mirrors were not known there till the commencement of the European trade with these remote regions. The former are still preferred in those countries, because they are not so liable to break, and can be preserved better in a dry hot climate than the amalgam of the latter.
Respecting the progress of this art, I know nothing more than what follows: – At first, melted lead, or perhaps tin, was poured over the glass plate while yet hot as it came from the furnace. This process agrees with that which, since very early periods, has been employed in or around Nuremberg for making convex mirrors by blowing with the pipe into the glass-bubble whilst still hot a metallic mixture, with a little resin or salt of tartar, which prevents oxidation and assists the fusion. When the bubble is covered all over in the inside, and after it has cooled, it is cut into small round mirrors. This art is an old German invention, for it is described by Porta and Garzoni, who both lived in the beginning of the sixteenth century, and who both expressly say, that it was then common in Germany. Curious foreigners often attempted to learn it, and imagined that the Germans kept it a secret. Boyle made various experiments in order to discover the process; and the secretary of the Royal Society endeavoured, by means of the ambassador from Charles II., who, perhaps about 1670, resided at Frankfort, to obtain a knowledge of it; but did not succeed, as we are told by Leibnitz199. It was called the art of preparing mirrors without foil; and it was highly esteemed, because it was supposed that it might be useful to those fond of catoptrics, by enabling them to form convex and concave mirrors themselves. This account of Leibnitz seems to have led Von Murr into a slight error, and induced him to believe that the art of making convex mirrors without foil was first found out at Nuremberg in 1670. I introduce this remark because I flatter myself he will not be displeased that I make the above service, rendered by his native city, to be a century and a half older. These small convex mirrors, which reflect a diminished, but a clearer image than our usual mirrors, are perhaps made still, though they are not now carried round so frequently for sale in Germany as they were thirty years ago, at which time, if I remember right, they were called (Ochsen-augen) ox-eyes. They were set in a round painted board, and had a very broad border or margin. One of them, in my possession, is two inches and a half in diameter. It is probable that the low price of plane mirrors, when glass-houses began to be more numerous, occasioned these convex ones to be little sought after. The mixture employed in making them was, according to Porta, antimony, lead, and colophonium; but according to Garzoni, it was una mistura di piombo, stagno, marchesita d’argento, e tartaro, which in the German edition is translated very badly, “lead, tin, flint, silver, and tartar.” The following observation perhaps is not altogether useless: Colophonium, which is employed on many other occasions for soldering, was formerly called mirror-resin, and was sold under that name even in the beginning of the present century. Frisch assigns no reason for this appellation, and Jacobson gives a wrong one, viz. its having a bright shining surface when broken. The true reason was the above-mentioned use; and as that is now very little known, it is called from that to which it is principally applied, violin-resin.
It appears that, instead of pouring melted metal over plates of glass, artists for some time applied to them the before-mentioned amalgam of tin, or covered them in some other manner, perhaps in the same way as Boyle covered concave glasses in the inside. Porta however saw almost the same process employed at Murano as that which is still followed at present. The tin, hammered to thin leaves, was spread out very smoothly; and quicksilver was poured over it, and rubbed into it, either with the hand or a hare’s foot; and when the tin was saturated it was covered with paper. The glass, wiped exceedingly clean, was then laid above it; and while the workman pressed it down with his left hand, he drew out very carefully with his right the paper that lay between the tin and the glass, over which weights were afterwards placed. This much at any rate is certain, that the method of covering with tin foil was known at Murano so early as the sixteenth century200, and therefore it is much older than J. M. Hoffmann supposes. To conclude, whether this ingenious invention belongs to the Venetians, as several later, and particularly Italian, writers assert, I can neither prove nor contradict; but it is well known that till about the end of the seventeenth century their mirrors were sold all over Europe and in both the Indies. After that period the glass-houses in other countries were improved, and new ones established; and the discovery made in France, that glass, like metal, could be cast into much larger plates than had been before prepared by blowing and rolling, was in more than one respect prejudicial to the sale of those made at Venice.
So early as the year 1634, attempts were made in France to establish glass-houses for manufacturing mirrors, and Eustache Grandmont obtained a patent for that purpose; but his undertaking was not attended with success. As Colbert exerted himself very much to promote manufactures of every kind, Nicholas de Noyer proposed to make mirrors according to the Venetian method. This plan was adopted by Charles Rivière, sieur du Freni, valet-de-chambre to the king; and having procured the royal permission, he sold it afterwards for a large sum to De Noyer, who, in 1665, received a confirmation of the patent, and an advance of 12,000 livres for four years, on condition of his procuring workmen from Venice, who, after serving eight years in the kingdom, were to be naturalized. De Noyer was joined by several more, who entered into partnership with him, and particularly by one Poquelin, who had hitherto carried on the greatest trade in Venetian mirrors, and who engaged workmen from Murano. The glass-houses were erected at the village of Tourlaville, near Cherbourg, in Lower Normandy. After the death of Colbert, who was succeeded by Louvois, the charter of the company was in 1684 renewed for thirty years longer, and at that period Pierre de Bagneux was at the head of it.
Scarcely had five years of this period elapsed, when, in 1688, Abraham Thevart made a proposal to the court for casting glass mirrors of a much larger size than any ever before made. This plan, after an accurate investigation, was approved; and in the same year he received the royal permission to use his invention for thirty years, but it was not registered till 1693 or 1694. The first plates were cast at Paris, and astonished every artist who saw them. They were eighty-four inches in height, and fifty in breadth. In order to lessen the excessive expense, the glass-houses were erected at St. Gobin, in Picardy; and to prevent all dispute with the old privileged company, Thevart was expressly bound to make plates at least sixty inches in length and forty in breadth, whereas the largest of those made before had never exceeded forty-five or fifty inches in length. On the other hand, the old company were allowed to make plates of a smaller size, and were prohibited from employing any of the instruments or apparatus invented