47 - Garnet Color.
You should have equal quantities of polverino and rocchetta frit mixed together thoroughly. For every 100 pounds of this frit, add 1 pound of prepared Piedmont manganese, as instructed in chapter 13, and 1 ounce of prepared zaffer, mixed well with the manganese. Mix this powder well with the above frit, and put it little by little into a crucible [in the furnace], being careful since the manganese makes the glass swell. Add it in slowly, so that the glass will not overflow.
Mix the zaffer thoroughly with the manganese and the colour will become enlivened and take on a glistening, graceful beauty. By the end of 4 days, the pot of glass will clarify and
colour nicely. With this dosage of manganese, work the glass to make cane for small pan-fired beads. For drinking glasses, and thin vessels the glass needs to be loaded more with colour.
In order to make thick cane you must diminish the amount of powder by about half the prescribed dose. In effect, you must Ioad the glass with more or less colour according to the pieces you plan to make. This falls to the discretion and guidance of whoever adds the powder with consideration that the glass should match the application.