Produced by bonding silver and copper sheets. The sheets of metal are placed together in close contact and heated under pressure with no intermediate joining material or solder. When silver and copper are heated in this way, limited diffusion between them will form a low melting point alloy at the interface, the alloy melting at around 780C, well below the melting point of either of the two pure metals. The earliest use of this technique dates from the 2nd millennium BC. However the common use in decorative objects dates from 1742 and was developed by Thomas Bolsover of Sheffield.