The art of glass shewing how to make all sorts of glass, crystal and enamel : likewise the making of pearls, precious stones, china and looking-glasses : to which is added, the method of painting on glass and enameling : also how to extract the colours from minerals, metals, herbs and flowers ... : illustrated with proper sculptures / written originally in French, by Mr. H. Blancourt, and now first translated into English ; with an appendix, containing exact instructions for making glass-eyes of all colours.

CHAP. XXIII. Another Way of making Ferretto of only Copper for Tinging Glass.

THis second way of making Ferretto is something more troublesome than the former, but its Effects in Glass are far finer. In this method you must take Vitriol instead of Sulphur, wherewith you stratifie the thin Plates of Copper in the Cruci∣ble just as in the precedent Chapter, then set this Crucible to Calcine in the Mouth of a Glass-Furnace, which the Italians call Occhio, and the French the little Working hole, where it ought to stand for the space of three days. Then take out the Crucible and add to the Copper new Rows or Layers of Vitriol, strati∣fying it as before; then you put the Crucible in a Reverberatory Fire in the same place as before; which you must continue to do for six times succes∣sively one after another, and then you will have a very Excellent Ferretto, which you beat to Powder, and it will tinge Glass of Extraordinary Beautiful Colours.