Mercury glass, also known as "silvered glass," is an antique decorative art glass produced by a few glassmakers in Bohemia, Engand and America from the mid 1800s through the early 1900s, notes AntiqueMercuryGlass.com. These are blown glass pieces that have a hollow interior, most of which are double walled. This hollow interior was coated with a silver nitrate solution. Originally mercury was used, but it was replaced with silver nitrate because of the problems and costs involved with using a mercury solution.
Determine what the item is. Objects made by the companies that produced mercury glass include English garden gazing balls, vases, candlesticks, religious items, doorknobs, curtain pins, sugar and creamer sets, salt cellars, bowls, compotes, goblets, salvers, hanging globes, globes on stands, reflectors for kerosene lamps and candles, Christmas ornaments and other types of novelties, decorative glass objects, and tableware.
Examine the bottom of the object. Silvered glass pieces have an opening in the bottom that was used for pouring the silver nitrate solution into and out of the vessel. The holes are often closed by a glass plug cemented in place or by a wooden cork covered with paper and wax, says the Weaton Arts and Cultural Center. The glass plug was often embossed with the name of the company that produced the object.
Look closely at the object to determine that there is a layer of silver lining the inside surface of the entire object. This is the most important aspect of mercury or silvered glass. The outside surface may have etched, embossed, painted or enameled decoration. Some companies in England occasionally produced silvered glass with a layer of colored lead glass over a layer of clear glass, with the silvering inside. Designs were then cut into the colored glass to allow the silvering to show through.