67 - Topaz Color in Lead Glass.
lnstead of polverino frit, use crystal frit in the amount of 15 pounds, and 12 pounds of Iead calx, as in the [recipe for emerald green]. Mix, fully sift, and then fuse these materials in a crucible. Do not expose them to excessive heat. At the end of 8 hours, empty it into water, and remove all metallic lead from the glass as well as from the crucible, as discussed at length for the green Iead glass [chapters 63, 65].
Return it to the crucible, and then repeat a second time, emptying it into water with the same diligence as before. To this glass, add half again as much of glass tin red a golden yellow colour, as is described in its place [chapter 71. leave it to incorporate and clarify. Then work it with the rules stated for the green. This mimics the colour of true oriental topaz.