Sand for copper medals
Recipe: Take hat felt burnt on a covered fire, iron dross, and burnt bone, all of which you should grind very finely, crush and spray with water and salt. Make a paste of it, mold it, and wipe it with hay fire. These three pulverized sands, having been very well refined on the porphyry slab, mold very well and cast well. Know that separately each of them is quite good. Burnt felt molds well and is removed quite neatly.
at left top margin of folio 083r
Plaster molds quite neatly but it swells. Bone does not have much body while iron dross does. Felt allows for an easy removal of the cast.