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

- - - - - folio image: 161r - - - - -

Preparing sand for box molds

at left top margin of folio 161r

After your sand [which is made] of gip de lateribus and alumen jameni is moulded as a core, gather the left—over pieces of your mold, and break them up on a long table with a big metal block until they are very well crushed. And for an even better result, sieve them neatly. Place them in the oven pots of tile—makers, in a bread oven, [firing them] several times, when it is well heated so that they become very red. When cooled down, rebreak them if you need to and sieve them. After, put them in a vaisse, a semal or a vessel that is appropriate and clean. And then wet it with clear water. And crush it and mix it with a big stick until it is very well—moistened and rinsed, and the dirty parts rise to the surface of the water. Keep stirring in this way the dulled gip, that one prepares to gilt burnished gold over five or six days, until it is in no way lumpy. And each time your stir it, leave it to rest and cull the clear water that will be on the top by tipping the pot, or with a porringer, or with a sponge. And put in some new clean water and in this way wash and stir until it is refined and purged of all filth. Then leave to drain a little bit and to dry and make of it some balls, soaked in sal ammoniac. Having been thus dried, put them to be recooked in very high heat in a reverberatory furnace for a good amount of time, where they will become very red. Having been recooked in this way, crush them and try to mold something in a box mold, having moistened your crushed powder with water of sal ammoniac. And reheat and redden you box mold, and if your sand comes away, then you must crush it again and moisten it again with water of sal ammoniac. Remold it in two balls and recook it and redden it and continue this for as many times as necessary until it does not come away from the box mold when the box mold is reddened. The main thing is for it to be well recooked, because otherwise the sal ammoniac will not calcinate well and will make the sand coarse. And for this reason, you should not put in too much sal ammoniac.