Excerpt from thesis entitled Techniques of Forging the Works of Art Made of Metal and Methods of Their Identification states that identification of forged patina does not always indicate the work is not authentic. The formation of natural patina on copper, bronze, lead, tin, and iron are discussed, as are the minute, natural impurities in metals or alloys which can help determine whether an item is forged. Methods used by forgers include the lost wax technique, the coating of surfaces with noble metals, and the mixing of techniques and alterations of original works to produce the so-called semi-forgeries of military accessories.