46 - To Make Golden Yellow in Glass.
Take 2 parts crystal frit made with tarso, which is much better than with sand, and 1 part rocchetta frit also made with tarso. Mix and remix these two frits well for every 100 pounds
of this composition, add 1 pound of tartar from the dregs of red wine. Use large pieces well vitrified naturally in bottles of wine, because the powder is no good. Crush these raw dregs well, and pass them through a fine sieve.
For every 1 pound of these dregs, add 1 pound of prepared Piedmont manganese, as instructed in chapter 13. Mix these two powders together well, and then thoroughly stir them in with the above-mentioned frit. Finally put it in the crucible, and leave it alone for 4 days over an ordinary furnace fire. However, because this powder makes the glass froth and swell, add it into the crucible nice and slow, so that the glass does not boil over.
Usually, at the end of 4 days you will see the glass is clarified , and nicely tinted. Now, work it into vessels or other pieces. With this close of material, it will be a most beautiful colour.
If you need less intensity in order to make thicker pieces, add somewhat less than the prescribed close of powder. For panfired bead-cane and similar things, delicate work, less than the prescribed dose of color would make them very pale and clear; therefore, a greater dose of material is called for. This will colour more strongly. For larger [ thick] spit beads, it is said that at Murano they reduce the dose of [wine] dregs and manganese by nearly half.
Take note to unite the crystal and rocchetta frits first, and mix them together thoroughly. Use the dregs of red wine, since that of white wine does not work well. Obtain it in large pieces, and not as powder, which also does not work well. Use manganese only from Piedmont. The powder is always given in parts, and given [to the frit], not to the fused glass, because then it will not tint.
With these rules and observations, you will make a very beautiful golden yellow, but it will be even nicer if you use all crystal frit. The yellow is even more beautiful and most attractive. This is the method I have used to make this colour many times, and it has always worked very nicely, every time l use it.