The Chemistry of Inks in Handwriting

C. Ainsworth Mitchell
1911 Scientific American  
BEFORE glvmg an account of some applications of chemistry in the direction of the general principles underlying the chemical methods of distinguishing be tween different kinds of ink in handwriting, I may, perhaps, be allowed briefiy to recapitulate the main outlines of the theory, and to add some details by way of illustration. Ordinary writing ink is essentially a mixture of a decoction of galls with a solution of copperas (ferrous sulphate), which slowly interact to form an iron tan nate
more » ... n iron tan nate that gradually becomes oxidized by exposure to the air, and gives the black pigment of handwriting. Characters written with a pure iron gall ink are nearly colorless when first put upon paper, and a con siderable time is needed for the insoluble black tan nate to be formed ,within the fibers. Prior to about the end of the eighteenth century, inks were exposed to the air or boiled, so that a par tial oxidation might take place within the fiuid, and thus give some depth of tint to the product before it was used for writing. The chief objections to such partial oxidation are that deposits are formed in the bottle, and prevent the ink fiowing smoothly from the pen, and that the fiuid has not the penetrating power of an unoxidized ink. Such inks, however, are still on the market, under the name of "Japan inks," but they are but . little used, their place having been taken by unoxidized inks, in which the black pigment is, as it were, in a latent condition, and a second pigment, such as indigo, logwood, or an aniline dye-stuff, is added to give a color to the writing pending the for mation of the iron tannate.
doi:10.1038/scientificamerican05131911-302supp fatcat:4d4nuoqwrjbrjabgixu7ank7by