Tom Arnold, I believe mercury/gold amalgam was used to gild objects, not to depletion gild.
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.
Richard Hart