Next infuse small Aleppo galls, slightly bruised in water. In two or three days, pour the liquor off.
By drawing a pencil dipped in this second solution over the characters written with the first, they will appear a beautiful black.
Invisible Gold Ink.
Put as much gold in as small a quantity of aqua regia as will dissolve it, and dilute it with two or three times the quantity of distilled water.
Next dissolve, in a separate vessel, fine pewter in aqua regia, and when it is well impregnated, add an equal quantity of distilled water.
Write your characters with the first solution: let it dry in the shade. To make them visible, draw a pencil or sponge, dipped in the second solution, over the paper, and the characters will appear of a purple colour.
Invisible Silver Ink.
Dissolve fine silver in aqua fortis; and after the dissolution, add some distilled water in the same manner as in the gold ink.
What is written with the above ink will remain invisible for three or four months, if kept from the air; but may be easily read in an hour, if exposed to the fire, air, or sun.