28 - To Make Thrice Baked Copper Scale with More Ease and Less Cast than Before
You should take copper scales, which are the flakes that the kettle-smiths make when they hammer pails, cups and other works of copper, that are hot worked in the fire. This flake, which falls from these works when they are struck, is called copper scale. It costs much less than solid copper, of which the scale described previously is made. In order to calcine it is not necessary to open and close the arches of the furnace, as in the previous recipe, which causes quite a bit of trouble and disturbance to the furnace.
Therefore, use this copper scale, that you have cleaned free of all dirt and filth, and washed with hot water many times to remove any sediment. What remains are the clean copper scales free from all contamination. At this point, put them in terracotta oven pans or on terracotta tiles, in the annealing chamber near to the 'eye', or even better in ovens made specifically for the purpose. In Pisa, I contrived to make a little oven in the form of a small frit kiln, in which at times I calcined 20 to 25 pounds of this copper scale and only in a few hours. But in the annealing chamber, near 'eye' of the furnace, you should leave it alone for 4 days, then tumble and grind it very well, passing it through a fine sieve.
Now return it to the terracotta oven pans, or tiles, as before with the same fire and heat for 4 days. lt will turn to a black powder and will lump together. Grind and sift it through a
fine sieve and again put it back on tiles and heat for 4 days. At this point, the copper scale will be optimally prepared without the annoyance and expense of the former method, and all in all, it will have the same effect in colouring. Take care to wash it thoroughly of all sediment before calcining it. As they say:
The sign will be that it makes the glass swell and boil, only then is it well prepared.