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What is Mercury Gilding/Silvering?

Mercury is a metal that is liquid at room temperature. When combined with gold or silver, it becomes viscous, its consistency becoming similar to that of butter. Mercury gilding is the process in which mercury is mixed with gold to make an amalgam that is applied to the surface of an object. (Mercury silvering uses the same process, but the mercury is mixed with silver.) When the object is then heated in an oven or over a fire, the mercury evaporates and leaves behind a thin coating of gold or silver. The evaporation process results in bubble-shaped cavities forming within the coating, requiring a final burnishing step to make it smooth.

Face of Bhairava
Face of Bhairava, c. 16th century
Mercury-gilded copper alloy with rock crystal, paint, foil, and glass
28 1/4 × 29 1/4 × 14 3/4 inches (71.8 × 74.3 × 37.5 cm)
Purchased with the Stella Kramrisch Fund, 1998
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Can Anything Be Mercury Gilded/Silvered?

Mercury-gilded/silvered objects must be fired in order to evaporate the mercury, which boils at 357 degrees Celsius. Only metals that are able to withstand this high temperature can survive the process. Another requirement is that the mercury amalgam must be able to sufficiently wet the entire surface of the material; otherwise the gold or silver will not adhere. For metals, the ability of the amalgam to stick is related to solubility. It may sound strange to talk about two metals being soluble in relationship to each other, but like other chemicals, mercury will only solubilize (dissolve) some metals, such as gold, silver, and copper. Therefore, for this type of gilding to work, the substrate must be composed primarily of metals that can be dissolved by mercury. The sixteenth-century Nepalese mask pictured at right was finished by mercury gilding a copper alloy.

Historical Use of Mercury Gilding/Silvering

The process of mercury gilding has been used for over two millennia. The earliest surviving examples of objects with gold coatings date from at least the fourth century BCE in China and the second century CE in Europe. Pieces with coatings produced by mercury silvering date from the first century in China and the eighth century in Europe. Today, mercury amalgams are more commonly known for their use in repairing dental cavities. In the eighth century in China and in the nineteenth century in Europe, dentists began making mercury amalgams—following techniques similar to those used for decorating metalwork—to create dental fillings.

Before electroplating was invented, mercury amalgams were the best choice for producing a smooth, thick coating of gold or silver on a three-dimensional object. The process also had the advantage of being able to be repeated until a coating of the desirable thickness was achieved. However, mercury gilding/silvering is rarely performed today due to its toxicity: when mercury evaporates during the heating process harmful vapors are released. In fact, this technique is illegal in many countries.

Eighteenth-century mercury gilding workshop. Etching from the Encyclopédie edited by Denis Diderot and Jean le Rond d’Alembert (Paris, 1763)

Detail from the etching above. Figure 1 is labeled as the craftsman who reheats gilded objects.
A selection of burnishing tools with agate tips. Figure 4 in the etching above holds a similar curved burnishing tool.

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