Mercury glass (or silvered glass) is glass that was blown double walled, then silvered between the layers with a liquid silvering solution, and sealed. Although mercury was originally used to provide the reflective coating for mirrors, elemental mercury was never used to create tableware. Silvered glass was free-blown, then silvered with a solution containing silver nitrate and grape sugar in solution, heated, then closed. Sealing methods include metal discs covered with a glass round or a cork inserted into the unpolished pontil scar. "Mercury" silvered glass was produced originally from around 1840 until at least 1930 in Bohemia (now the Czech Republic), Germany and also manufactured in England from 1849 to 1855. Edward Varnish and Frederick Hale Thomson patented the technique for silvering glass vessels in 1849. The English examples were often cased with a layer of colored glass then cut to silver as illustrated in the photograph.