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Spalt

Spalt is white like cooked plaster and one can find it in mounds and stones made in long stairs and long veins. It is very soft such that with a fingernail and it makes a powder like that of our chalk from Champagne. And because everything which is provided from the earth is mixed with some other substance, to purify it [the spalt], one boils it with somewhat large gemstones then tempers it with essence of sal ammoniac. One puts [a lump of it] the size of a walnut in a large bottle of water and <div class="folio" align="center">- - - - - 108v - - - - - </div>that way one tempers it & reducing it into small balls, [one] purges it of impurities [by] then putting it on to cook cleanly in a vessel of earth[enware] in a furnace like those in which pots [are made] and one leaves it there to the point at which pots would be fired. After one tempers it more with essence of sal ammoniac & boiling it very strongly and emptying the murky water & putting it in a separate vessel straight after put back the same water over it & one boils & one puts back the murky water again with the other. And one does this therefore until that which is there has passed away. In this way one purges and purifies and makes it a very fine and malleable [matter]. After one has taken away the water by tilting [it] or with a sponge, one takes the residue and dries it. Then moistening it with the aforementioned water the way one did with the other sand, one uses it in a frame or if it shrinks [this] is a sign that it is not fired enough & needs to be fired more. This one is proper for molding all metal and especially gold and silver and the more it is used the better it is. One should put alum which you have cast of lead or tin separately because it makes gold. sour if you cast it there.