087v - - - - - Sand, slate, and burned earth
Very burnt sand loses its bond. Slate is reheated & molds neatly. Next, it is true that often it becomes porous, like burned earth also does, like fat sand also does.
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I find that one ought not to knowck on very finely ground sands, for it shakes them loose, & make prevents them from releasing neatly. But one ought to press hard and moisten them sufficiently.
Magistra
Founders take the roots of a young elm when it has sap, & boil it in wine, or better yet vinegar, and keep it all year long in a cask.
Sand from the mine of Thoulouse
Casting sand coming from the mine, once passed through a double sieve, next put in with melted resin, burns & inflames & becomes all red & inflamed like iron. Once cold it is completely black and can be ground very finely on porphyry. Thus having prepared it & render it without asperity on the fingernail, I moistened it with beaten egg glair & beat it well, until it was not pasty but rather powdery. I found it of very good release, & molded with it in lead & tin very neatly, but it wants to be well reheated & at ease.
Others beat it well in a mortar, in small amounts at a time, & thus it detaches and renders very finely. Then they reheat it moderately, only to dry it. Then they grind it dry on porphyry. And thus it becomes as if impalpable, and not too dried out, it and it retains body & bond of the earth of which it is related, and is better than when it is very burnt. Once moistened with egg glair wiped with a sponge, it releases very neatly M very neatly in low relief, but not for figures in high relief. Therefore, since then I experimented lexper with moistening it only with very strong vinegar. It released a figure which I could not release previously. And I believe that, moistening the finest in the same way like with glair & the lumpiest, to fill the chasses with salt water or wine, that they do not ally so well. Since they are of the same nature & are moistened the same, they embrace each other, & hold together one with the other.
To mold well, after having prepared your sands, mold in a day. Slowly reheat them the next day, then cast them on another.
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One ought to choose the one which is usually as in clods & lumps, well deep in the earth, for usually the one that is found above has too much earth, and the deep one is similar to rock.
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I have molded with it in pure lead very neatly hot, & I had as an example the first very neat one, but the vinegar hardly gives it any bond, & thus it withstood only one cast.