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Powder for hourglasses

It must be made very fine and not subject to rust and with enough weight to flow. Taking i lb. of lead, melt it and skim and purify it from its filth, then pour into it four ℥ of finely ground common salt, and take care that there are no stones or earth. And immediately after pouring it, stir continuously very well with an iron tool until the lead and salt are quite incorporated, and take it immediately off the fire, stirring continuously. And if it seems too coarse, grind it on a marble slab and pass it through a fine sieve, then wash it as many as times as necessary until the water runs clear, throwing out the fine powder that will float on it, renewing the water as many times as necessary until it is completely cleared.