53 - An Even Prettier Black.
To 100 pounds of rocchetta frit, you should add 2 pounds of pulverized red wine dregs and 6 ounces of manganese powder. Mix this frit with the dregs, and put it into the furnace [crucible] nice and slow, because it will froth quite a bit. Then leave the glass to clarify, which will take approximately 4 days. Now stir the glass well, and wash it. You will have a black fit for any job, and more marvellous than all the other blacks of which I have written.