Fire-gilding is the best technique for bronze gilding in terms of quality and durability. It is also the oldest technique. The amalgam gold (24 karats) and mercury enables a thick coating of gold (about 4 to 5 microns). This amalgam, with the aid of fire, enables the gold to penetrate into the pores of the metal trapping a portion of the gold (which is not the case with electroplating). This is the reason why fire-gilding is very resistant. The gilding can be preserved for centuries with this technique.
Here is the process for fire-gilding. First, the amalgam gold and mercury is made (1). Then the amalgam is spread on the object to be gilded (2). Next, the object is heated on a charcoal fire until the mercury is completely evaporated (3). Once the objet is gilt, the gold is smoothed by a scratch brush of brass wire. Following the gilding process is the burnishing. With a hematite stone, the gold is crushed in certain areas in order to create contrasts between the shiny and unlustrous parts (4). The final step is the "mise en couleur" or patina in order to give the gilding the desired tone.