Mirrors During the Reinassance Period
By Helen Costantino Fioratti
After many forests were depleted for fuel and manufactory and wood became scarce, many of the glass producers in France switched to coal as mentioned by C.A. Swimburne .
The coal produced in France was noted by another Swinburne who watched the barges going down the Loire river from Rouen which he said were loaded with ‘a bad kind of coal’.
Samuel Johnson (1709-1784) wrote of a trip around Britain, regarding imported glass: “We went to see the looking glasses wrought. They come from Normandy in cast plates, perhaps the third of an inch thick. At Paris they are ground upon a marble table, by rubbing one plate on another with grit between them. Of the various sands, of which there are said to be five, I could not learn. The handle by which the upper glass is moved has the form of a wheel, which may be moved in all directions. The plates are sent up with their surfaces ground, but not polished, and so continue till they are bespoken, lest time should spoil the surface, as we were told. Those that are to be polished are laid on a table covered with several thick cloths, hard strained that the resistance may be equal; they are then rubbed with a hand rubber held down hard by a contrivance which I did not well understand.
The powder which is used last seemed to me to be iron dissolved in aqua fortis. They called it, as Baretti said, Mar de l’eau forte, which he thought was dregs. They mentioned vitriol and saltpeter. The cannon ball swam in the quicksilver. To silver them, a leaf of beaten tin is laid, and rubbed with quicksilver to which it unites. Then more quicksilver is poured upon it, which by its mutual attraction rises very high. Then a paper is laid at the nearest end of the plate, over which the glass is slided till it lies upon the plate, having driven much of the quicksilver before it. It is then I think pressed upon cloaths, and then set sloping to drop the superfluous mercury. The slope is daily heightened towards a perpendicular.”