1/2" or larger Cast bronze ruby cabochon set in a pendant any listed seal on it. These are the strongest Demon seals from what I have found. The grimoirium Verum for example states to use ruby or emerald for the seals, and with very good reason. These are most definitely stronger than metal, parchment, or even semi-precious stones. The ruby seals can be used as an extremely strong conact point, or as a reward, trade or thank you, for work done by the Daemon Demon.