Quotation from: The Notebooks of Leonardo Da Vinci
Written by: Leonardo da Vinci
613.
Chalk dissolves in wine and in vinegar or in aqua fortis and can be
recombined with gum.
614.
PAPER FOR DRAWING UPON IN BLACK BY THE AID OF YOUR SPITTLE.
Take powdered gall nuts and vitriol, powder them and spread them on
paper like a varnish, then write on it with a pen wetted with
spittle and it will turn as black as ink.