The term ‘ormolu’, adapted from the French words or moulu (meaning ground gold), refers to decorative objects and mounts for furniture and porcelain, made of copper, brass and bronze and gilded by the process of mercury gilding. The term, which was introduced into England in the early 1760s, usually refers only to pieces dating from after the mid-17th century.

Mercury gilding involves reducing the gold to a powder and amalgamating it with mercury at a high temperature. The proportions are usually six parts of mercury to one of gold. On cooling, the gold amalgam is squeezed through chamois leather, to remove any excess mercury. This leaves a paste with the consistency of butter that is roughly two parts of mercury to one of gold. The surfaces of the metal to be gilded are cleaned thoroughly with nitric acid and smeared with mercuric nitrate. The amalgam is then applied with a brush or gilding knife, and the object is heated until the mercury has evaporated, leaving the gold bonded to the surface. Surfaces that need to be coloured further can be reheated or treated with various chemicals, with areas matted or burnished as desired.

Because mercury vapour is toxic, the average life expectancy for a gilder in the 18th century was just 30 years. The process is banned today except under carefully controlled conditions, and has been replaced by electrolysis.