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

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Iron engravers’ varnish

Take linseed oil or walnut oil and instead of black pitch you will add some pine resin and you must cook it like black varnish on fire. And to apply it, heat your iron and apply just one layer of varnish, and when it no longer smokes, it is dry. Then engrave with a steel point whatever you want. Then take some salt and verdigris and soak it with as much of one as of the other in very strong vinegar, and leave it for XX4 hours before using it, and the whole will be soaked. Then spread this liqueur or sauce on the engraved object with a sponge

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or linen cloth and leave it thus for xx4 hours and it will be engraved. But if you should want to engrave it quickly, varnish all your work and boil it in the aforementioned liquor, and this will engrave it quickly.