Burnishing, also known as metallodising, is a chemical treatment that darkens the surface colour of a metal. There are two variants, hot and cold, which are carried out in different ways.
It is a very old practice, but the rudimentary processes of the past have been progressively perfected until today. The first chemical burnishing process ever described in Europe dates back to the second half of the 18th century, reported in the German magazine Hannover Magazin and focused on firearms.