White boiling

White boiling is a process used to beautify low-value silver goods made from an alloy with a high copper content .

The workpieces are kept in glowing coal fire until they are provided with a black coating on the surface as a result of the oxidation of the copper contained in the alloy . The less noble copper is then removed by heated, dilute sulfuric acid or a tartaric solution and a thin layer of silver remains on the surface.

The older divisional coins were “boiled white”, so they appeared silver-white as long as they were new. During use, the pure silver was rubbed off on the surface and the reddish color of the copper-containing alloy came to light.

White boiling is also known as “ wet tinning ”.