The casting mold is used at the Foundry to craft items. Each mold has 32 durability.
Any undamaged tool or armor, as well as buckets and rails, can be used to imprint the mold with a template that can be used in the foundry. The item also needs to lack any NBT data. The item is not consumed in the process.
While diamond tools can be used to create mold imprints, the foundry cannot craft diamond tools as diamonds are not "ingots."