Ormolu

Ormolu /ˈɔːrməluː/ (from French or moulu, signifying ground or pounded gold) is an English term, used since the 18th century for the technique of applying finely ground, high-carat gold–mercury amalgam to an object of bronze, and for objects finished in this way.

Process

The mercury is driven off in a kiln leaving behind a gold-colored veneer. The French refer to this technique as bronze doré; in English, it is known as "gilt bronze".

The manufacture of true ormolu employs a process known as mercury-gilding or fire-gilding, in which a solution of nitrate of mercury is applied to a piece of copper, brass, or bronze; followed by the application of an amalgam of gold and mercury. The item is then exposed to extreme heat until the mercury burns off and the gold remains, adhering to the metal object.

Health risk

Due to exposure to the harmful mercury fumes, most gilders did not survive beyond 40 years of age. In literature there is a reference from John Webster—

After around 1830 the legislation in France had outlawed the use of mercury, although it continued to be commonly employed until circa 1900 and even was still in use around 1960 in very few workshops. To replace ormolu, other gilding techniques (like electroplating from the mid-19th century on) were utilized instead, but nothing surpasses the original mercury-firing method for durability, sheer beauty and richness of colour.Electroplating is the most common modern technique. Ormolu techniques are essentially the same as those used on silver, to produce silver-gilt (also known as vermeil).