Solid gold bars. That or top quality stainless steel bars properly passivated and polished. The correct question is what material is near worthless and not us

Solid gold bars. That or top quality stainless steel bars properly passivated and polished. The correct question is what material is near worthless and not usable as a construction brick that is none the less durable and laser engravable. Its going to be hard to beat clay bricks.