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

- - - - - folio image: 111v - - - - -

Composition of sand

Everything being baked thoroughly as said above, take four 4 molds full of plaster, two 2 of brick, and one of alum de plume. Do not pass through the sieve to mix, because the alum would not go through. Mix it with your hands until neither one nor the other, neither white nor red, may be distinguished from the other. If your plaster is not strong, do not mix in as much alum de plume because it softens molds. Make sure too that your sand is not hot (since it has been baked thoroughly recently) when you will want to mix it with water, because that makes molds too soft and breakable.

atĀ left bottomĀ margin of folio 111v

You may sometimes decrease the quantity of plaster if you do not find it strong enough to resist fire and if it splits, so that the proportion of crushed tiles sustains it, with the alum de plume, which you can also increase so that it creates a better bond.