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sdo:abstract
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"Furthermore, if you wish to make a green of Rouen, take some sheets of very pure copper, and smear them all over with the best soap, and put these sheets into a clean vessel, made for the purpose, and fill it with pure vinegar. But arrange the sheets above it, in such a way that they may not come into contact with the vinegar. And when you have covered the vase, seal it doubly; and at the end of one month open it, and scrape what you find on the copper sheets into a dish, and dry it."
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