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

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For whitening ceruse

Hard—boil some eggs, cut them in half and take the yolks out, and between the two halves of the white put a bit of ceruse, and tie the two halves together with thread. Then boil in clear water, and it will become black, and thus the ceruse will be purified. Some reheat it over fire and it becomes very white.