Double Ingots, are produced by welding two Ingots of the same metal together on an Anvil. To weld, both ingots must be placed in the welding slots of an anvil at weldable temperature, and the anvil must be supplied with Flux.
For compatibility reasons, double ingots can be made from any metal. However, not every double ingot has a valid use. If you make a useless double ingot, it can be recycled back into molten metal in a Crucible