Put some litharge into strong distilled vinegar, and let it stand for twenty-four hours; then strain it off, and, after it is quite settled, put it into a bottle closely corked, and preserve it for use. Having done this, put into a pint bottle two ounces of quicklime, one ounce of orpiment in powder, and as much water as will rise two or three fingers' breadth above them; and when the solution is made, pour the liquid gently off, and let it stand in the sua for two or three days, observing to turn it five or six times each day.

When these liquors are ready for use, any letters written by the first, being exposed to the vapours of the second, will quickly become visible; and if you would have them disappear again, you must draw a sponge, or pencil, dipt in aquafortis, or spirit of nitre, over them: and if, after this, you would have them appear again, stay till the paper is quite dry, and then pass the vivifying liquor, made of the solution of orpi-ment, over them, as before.