Quotation from: The Notebooks of Leonardo Da Vinci

Written by: Leonardo da Vinci


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.

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