Emery in large grains may be broken by putting it on a cloth many
times doubled, and hit it sideways with the hammer, when it will
break up; then mix it little by little and it can be founded with
ease; but if you hold it on the anvil you will never break it, when
it is large.

Any one who grinds smalt should do it on plates of tempered steel
with a cone shaped grinder; then put it in aqua fortis, which melts
away the steel that may have been worked up and mixed with the
smalt, and which makes it black; it then remains purified and clean;
and if you grind it on porphyry the porphyry will work up and mix
with the smalt and spoil it, and aqua fortis will never remove it
because it cannot dissolve the porphyry.

If you want a fine blue colour dissolve the smalt made with tartar,
and then remove the salt.

Vitrified brass makes a fine red.

729.

STUCCO.

Place stucco over the prominence of the..... which may be composed
of Venus and Mercury, and lay it well over that prominence of the
thickness of the side of a knife, made with the ruler and cover this
with the bell of a still, and you will have again the moisture with
which you applied the paste. The rest you may dry [Margin note: On
stucco (729. 730).] [Footnote: In this passage a few words have been
written in a sort of cipher--that is to say backwards; as in l. 3