Making and Knowing
A minimal edition of BnF Ms Fr 640 in English Translation

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Crocum ferry

After I processed it with vinegar and reddened under heat, I had it ground very finely on the porphyry, until there could be no ruggedness felt under the nails. Then I soaked it in very good vinegar for 2 or 3 days, stirring the mixture several times a day. Then I boiled it and made it red—hot in a pot, and put the whole thing into an air furnace. I obtained a mass full of eyes, but that crumbled finely between the fingers. I mixed half as much as stone alum in the sand. I diluted the sand very thinly, and molded a very small lizard, which molded very cleanly and finely. Crocum ferry does not make the mold harder, but makes it firmer. When your mold is soft and fat under your nail, it means that the crocum is good, very fine and well prepared. You can add any quantity of crocum, your mold will not be damaged because it is a friend of gold. I think it would be the same with silver. And in order that molds made with it do not crack, make it with needle filings.

at left top margin of folio 132v

Sand is better made with distilled vinegar.

at left middle margin of folio 132v

You can add this sand to the molds you want to use to cast silver, because it make molds firmer, and when you scratch it, you will find it a bit rougher than the other molds not made from this sand. You mold very clean with this sand.

at left bottom margin of folio 132v

You can use this one for all molds, because it prevents them from cracking and bursting when heated. This sand withstands several casts for molding flat medals. Sand from steel or needle filings is redder and better.