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

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Sand from sand pit from Toulouse

In order to use sand from a sandpit for casting, filter it through a double sieve, then having mixed it with molten resin it burns and heats, and becomes all red and hot as iron. Once it has cooled down it is completely black and can be pulverised on porphyry very well. Having prepared it like this and checked the smoothness of the surface with my nail, I moistened it with egg white and beat it vigorously, until it was not a paste anymore but a powder. I found this sand to release the cast very well, and molded very clean in lead and tin with it, however it needs to be reheated and at leisure.

Others beat it strongly in a mortar, in small amounts at a time, thus it detaches and comes out very fine; then they bake it moderately, just enough to dry it, and then they crush it dry on porphyry. Thus it is made almost impalpable, and yet not too dry , and it retains the consistency and the binding quality of the earth to which it is related, and is better than when it is burnt. When you moisten it with egg white and pass it through a sponge it releases very clean for a low relief, but not a figure in high relief. Considering this, since then I experimented with moistening it only with strong vinegar. That way it releases a figure I previously had not been able to release from the mold. I think that even when you wet the finest sort with egg white, or in a similar fashion, or the thick sort to fill chasses with water, salt, or vinegar, they do not mix so well. However, given that they are of one and the same nature, and are similarly moistened, they espouse each other, and hold together.

To mold well, when your sands are prepared, mold in one day. Bake slowly the next day, then cast the other.

at left middle margin of folio 087v

It is necessary to choose sand that like comes in clods and lumps, and deep down in the earth, because commonly the one near the surface is too much akin to earth, whereas the deep one is similar to rock.

at left middle margin of folio 087v

I have sometimes molded with pure lead cast very clean hot, and the example as well as the principal were very clean, but since the vinegar gives it little binding, it held only for one cast.