Many documents that have been written with bad ink after a certain time fade, especially if they have been kept in a damp place, or if the paper that has been used has been over-bleached in its manufacture. Sometimes ship letters get wetted with sea water, and many other causes obliterate writing that is of much value. In nearly all instances such writing may be restored, or at least rendered legible, by brushing over the half distinct lines with a solution of prussiate of potass with a camel's hair pencil. The solution may be made by dissolving about half a tea-spoonful of prussiate of potass in a tablespoon-ful of boiling water. For certain chemical reasons this does not answer in all cases, and when it fails we may use the following with good hopes of success :First, a strong infn' son of tea, made with a teaspoonful of black tea in half a cup of boiling water; or, secondly, a solution of carbonate of soda made in the same manner ; or, thirdly, a quarter of an onnce of protosnlphate of iron (green vitriol) in a like qnantity of water. A last resource is a solution of sulphuret of potassium (liver of potash) ?f about the same strength as the preceding solutions. In trying to restore writing, we ought to begin with only one or two words, because if the first solntion does not answer, we then have an opportunity of trying the others successively until we discover which answers best ; but, as a general rule, it may be relied on that the first-named is the most likely. These trials are equally adapted for writing upon parchment as on other material. S. Piesse.
This article was originally published with the title "To Restore Writing" in Scientific American 13, 47, 371 (July 1858)