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

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at middle margin of folio 106v

If the plaster is mixed with some dust or is not the hard kind, […] in the fire and make […]”

at left top margin of folio 106v

Plaster When you have it in stone form, choose the hardest pieces and those which do not easily break into small pieces with your nail, and clean it well of powder & filth rather than crushing them with it.

at left middle margin of folio 106v

Plaster alone does not sustain […] but breaks up into lumps. Keep reheated plaster, as is said here, one or two months well compacted in a dry place, if it’s not the rainy season but rather fresh out it is more excellent for exquisite work.

at left middle margin of folio 106v

It must maintain its fire and turn red like lit charcoal.

at bottom margin of folio 106v

Stone alum is that which binds well to sand.

at bottom margin of folio 106v

Crocum ferri is fit for gold. It is this which, mixed into sand, breaks it up again & keeps it hot.

The hardest plaster, as was said, is the best, being taken thusly totally raw from stones of this kind. Crush it as finely as possible and pass it through the most fine sieve or sleeve that you can. Having been made fine in this way, put a good amount in a cauldron or frying pan over an open flame. & as it starts to heat up, stir it continuously. And heavy and lumpy though it is, it will become so light and so tractable that it will appear to you not to have any resistance to the said stirring, as though it were of water. Continue to keep stirring it continuously until it returns once again to being heavy and thick. And now this is the sign that it is cooked, but do not reheat it at all such that your stone alum brick be reheated & that clay circles form. Because this must be the last reheating, and when everything else is ready, because the less that the plaster remains reheated & the more suddenly it is put into the work, the better, because it takes rather better. It is not permitted to reheat it except when you want to mold. And to reheat it, put it, in fine, totally raw powder, in a cauldron on a clear flame & do not give it too much [heat] in one go nor too fierce. Stir continuously with a long stick, turning around the cauldron to avoid the vapor. And in the middle, in the form of a figure 8 at the beginning, you will find it heavy [and] clayey because it is full of moisture, [and] when it heats up, it will start to throw off [the moisture] in some bubbles on the edges of the cauldron. And finally it will become liquid & mealy and like bran and start boiling in the middle. Continue to stir continuously until you recognize that it has once again become heavy ʘʘ

- - - - - folio image: 107r - - - - -

Figure Figure

as heavy as before, and it should be like a paste not very thick, it must not be as easy to stir as a liquid. This state shows you that it is cooked enough. It must boil in the middle, and all around you must have a thick mixture. If you reheat it too much your mixture would be short of body, because if it becomes red the mixture will lose its strength and it will spoil the sand. Let it cool before mixing it to any other sand. […]