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

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They melt orpiment entirely in a glass bottle on very hot ashes, but it would be more appropriate to sublimate orpiment in a long—neck matrass as for making garnets. The orpiment thus turns red like red enamel and it has to be ground first in distemper, because once entirely melted it is very brittle and difficult to grind. Then, once dry, you can thin it with oil and it will make a deep and saturated yellow. But to prevent orpiment from fading in contact with other colours and make it compatible with these and to make it dry quickly, a most rare secret is to calcine common salt and to grind it together with the orpiment. Green verditer is not used with oil.