XVII. MIRRORS, GLASS PICTURES, GLASS KNOBS
Mirrors more properly come within the category of furniture, but they largely consist of glass, of course, so that some notice of them is needed here.
In 1688 the art of casting large plates of glass began to be carried on in France. In 1663 the art had been patented in England, but for smaller sizes. One French mirror, now in the Louvre at Paris, was valued at £6000 in 1791. Glass used to be a costly product; the chief reason why old prints are usually found trimmed of their margins was that glass to frame with them was so dear.
Old mirrors with bevelled edges have the bevel flattish, nearly in the plane of the glass; the bevel follows the shape of the frame, but is irregular at its inner outlines, because the grinding of the bevel was done by hand. Modern bevels, done by machinery, are almost mathematically exact, and make an acuter angle with the frame than the old bevels do. Also the silvering at the back of old mirrors differs from the method of silvering now used; the difference is much more easy to recognize by the eye than to describe, but there is a kind of granulation in the older backing.
Glass pictures are of two kinds; one in which the painting, in oil-colours, was done upon the glass itself, usually at the back of it; and another in which the paint was laid on coarsely behind a print which, rubbed very thin at the back of the paper, had been affixed to the back of the glass. This second kind is the more numerously met with; also it is the most counterfeited. Age may be known, however, by the curving, bubbly surface of the glass. A third kind, consisting of a mosaic of bits of glass, so laid together in cement as to form a picture is rare, even in modern examples.
Glass knobs to handsome sideboards were used in the first quarter of the nineteenth century, and have continually been used in Yorkshire, for dressers, since then; old glass knobs are usually moulded, but some are cut, though the round, uncut shape was the most convenient for handling. Glass door-knobs are found.