Armor was embroidered during the Medieval period by using oil and lead paint to mark off ornate areas which would stand out and perhaps be decorated with gold or other precious metals in a process referred to as “gilding”. Gold does not easily bind to any type of metal and the only way to properly do so is to undergo a process which involves mixing the gold with mercury. Once applied, a mixture of salt, vinegar, and copper sulphate, which is root killer, makes a paste which eats through the metal leaving the painted parts untouched, and resulting in an etched piece of armor. Blacksmiths sometimes heat treated armor which turned it a blueish hue which essentially rusts the metal as it is referred to as an “oxide” and an oxide occurs when a metal comes into contact with oxygen which reacts with the metal and creates a deposit when heated to a very specific temperature, as the heat is what shifts the red color of rust to the blue area of the color spectrum