OF GRINDING GOLD FOR BOOKS, AND OF CASTING THE MILL.
When you have traced out figures or letters in books, take pure gold and
file it very finely in a clean cup or small basin, and wash it with a
pencil in the shell of a tortoise, or a shell which is taken out of the
water. Have then a mill with its pestle, both cast from metal of copper
and tin mixed together, so that three parts may be of pure copper, and
the fourth of pure tin, free from lead. With this composition the mill is
cast in the form of a small mortar, and its pestle round about an iron in
the form of a knot, so that the iron may protrude of the thickness of a
finger, and in length a little more than half a foot, the third part of
which iron is fixed in wood carefully turned, in length about one yard,
and pierced very straightly; in the lower part of which, however, of the
length of four fingers from the end, must be a revolving wheel, either of
wood or of lead, and in the middle of the upper part is fixed a leather
strap, by which it can be pulled, and, in revolving, be drawn back. Then
this mill is placed in a hollow, upon a bench fitted for it, between two
small wooden pillars firmly fixed into the same bench, upon which another
piece of wood is to be inserted, which can be taken out and replaced, in
the middle of which, at the lower part, is a hole in which the pestle of
the mill will revolve. These things thus disposed, the gold, carefully
cleansed, is put into the mill, a little water added, and the pestle
placed, and the upper piece of wood fitted, the strap is drawn and is
permitted to revolve, again pulled, and again it revolves, and this must
so be done for two or three hours. Then the upper wood is taken off, and
the pestle washed in the same water with a pencil. Afterwards the mill is
taken up, and the gold, with the water, is stirred to the bottom with the
pencil, and is left a little, until the grosser part subsides; the water
is presently poured into a very clean basin, and whatever gold comes away
with the water is ground. Replacing the water and the pestle, and wood
above being placed, again it is milled in the same way as before, until
it altogether comes away with the water. In the like manner are ground
silver, brass, and copper. But gold is ground most carefully, and must be
lightly milled; and you must often inspect it, because it is softer than
the other metals, that it may not adhere to the mill or the pestle, and
become heaped together. If through negligence this should happen, that
which is conglomerate is scraped together and taken out, and what is left
is milled until finished. Which being done, pouring out the upper water
with the impurities from the basin, wash the gold carefully in a clean
shell; then pouring the water from it, agitate it with the pencil, and
when you have had it in your hand for one hour, pour it into another
shell, and keep that very fine part which has come away with the waters.
Then again, water being placed with it, warm it and stir it over the
fire, and, as before, pour away the fine particles with the water, and
you may act thus until you shall have purified it entirely. After this
wash with water the same refined part, and in the same manner a second
and a third time, and whatever gold you gather mix with the former. In
the same way you will wash silver, brass, and copper. Afterwards take the
bladder of a fish which is called _huso_ (sturgeon), and washing it three
times in tepid water, leave it to soften a night, and on the morrow warm
it on the fire, so that it does not boil up until you prove with your
finger if it adhere, and when it does adhere strongly, the glue is good.