124 - Rosichiero to Enamel Gold
Have crystal frit made in the following manner: take 10 lbs of polverino salt, and 5 lbs of white tarso, ground most finely like flour. Make a paste of this material with water, so that it
is a hard paste, and make it into small flat cakes. Put these in an earthen pan set into a small furnace made in the form of a limekiln, and calcine them with a good fire for 10 hours. Then move them to the neglected area of the furnace, near the eye, for 3 or 4 days until they fully calcine.
You should have calx of lead and tin, that is to say its finer parts. You should separate it with water, as demonstrated in the sixth book about enamels, in the chapter [93] about enamel base material. Take 2 lbs of this purified calx, with 2 lbs of calcined white wine tartar, mix everything thoroughly, and put it in a crucible glazed with white glass. Leave it to fuse and clarify well.
When it is ready, throw it into water, and then return it to the crucible to clarify. Throw in water a second time, reheat, and when it has clarified well add 10 oz of red copper to the crucible. Leave it to digest the colour well, and then give it iron crocus made with aqua fortis [chapter 18]. Add this crocus little by little, just like manganese, and then leave it to rest for
6 hours, and watch to see if the color is good. If not then give it more of the crocus, little by little, enough to give the desired colour.