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

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Rock and grotto

You need to grind white and yellow marcasites & various kinds of ores. Wash them thoroughly, so the soiled and chalky end will be clean, in order that only the lustrous grain of the ore will be left, from which you will powder your rock previously covered with strong glue, if your grotto is not used as a fountain and touches water. You will thus obtain a nice work.