These inks contain carbon black, and therefore absorb light with wavelengths in the range of 300 to 1000 nm. When chemical liquid 867A, a milk-white liquid, is applied with a small brush to a document on which the original writing has been covered with a layer of ink, the writing becomes legible in a few moments and is the same color as it was originally. When chemical liquid 867B, a colorless and transparent liquid, is applied to the back side of a document, the original writing is revealed in its true colors. Both chemicals produce readable documents that can be kept for long time periods. These chemicals have been used in both criminal cases and for revealing historical documents. Photographs. (Author abstract modified)