What is Mercury Glass?
Mercury glass, also known as silvered glass, contains neither mercury nor silver. It's actually clear glass, mold-blown into double-walled shapes and coated on the inside with a silvering formula, which is inserted though a small hole that is then sealed with a plug. A few manufacturers did, for a time, try to line their glass with a mercury solution; this practice was discontinued due to expense and toxicity, but it helps explain the origin of the misnomer.

First discovered in early-19th-century Germany, mercury glass was used as an inexpensive and tarnish-free substitute for silver in such objects as candlesticks and doorknobs. It then gained favor in France and England, where it was made into useful household wares like vases and goblets, and in America, where it was turned into glass vases, goblets, tankards, sugar basins, tumblers, and even spittoons. Some critics condemned it for "looking too much like mirror and too little like silver," which is precisely what people liked about it. At worst, mirror attracts a few vain glances, while genuine silver attracts thieves. Appreciation for the inexpensive baubles rose, until the advent of the lightbulb: in "modern" light, no burglar would mistake glass for silver.