Ormolu (from French or moulu, signifying gold ground or pounded) is an 18th-century English term for applying finely ground, high-karat gold in a mercury amalgam to an object of bronze. The mercury is driven off in a kiln. The French refer to this technique as bronze doré, in English 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 was then exposed to extreme heat until the mercury burned off and the gold remained, adhered to the metal object. Most mercury gilders died by the age of 40 due to exposure to the harmful mercury fumes.

Hang him; a gilder that hath his brains perished with quicksilver is not more cold in the liver

—The White Devil, John Webster

Mercury gilding was outlawed from the 19th (in France) or 20th centuries because of its health risks, and electroplating is the commonest modern techique. Ormolu techniques are essentially the same as those used on silver, to produce silver-gilt (also known as vermeil).

A later substitute of a mixture of metals resembling ormolu was developed in France and called pomponne, though, confusingly, the mix of copper and zinc, sometimes with an addition of tin, is technically a type of brass. From the 19th century the term has been popularized to refer to gilt metal or imitation gold.

Gilt-bronze is found from antiquity onwards across Eurasia, but especially in Chinese art, where it was always more common than silver-gilt, the opposite of Europe.