Sal ammoniac and iron dross
I pulverized sal ammoniac, previously well dried in a hot bronze mortar over heat. Then I filtered the salt through a double sieve; it became very fine. But to make it finer, I dry ground it on the porphyry, then I mixed it with iron dross which was pulverized and ground the same way. Both ingredients take a very clean cast of bas—reliefs, without being moistened with serain, or into the hollow mould, or anywhere else with the serviette, and the cast can be cleanly removed.