CHAPTER VIII
DISTINGUISHING INKS IN HANDRWRITING
Elizabethan Ink—Milton’s Bible—Age of Inks—Carbon Inks—Herculaneum MSS.—Forgery of Ancient Documents.
In order to make clear the principles upon which are based the methods of distinguishing between different kinds of ink in handwriting it is necessary to give some account of the nature of ink.
Ordinary writing ink is essentially a mixture of a decoction of galls (or other substances containing tannin) with a solution of copperas, or as it is now termed, ferrous sulphate. These substances combine with one another to form a tannate of iron, which gradually changes on exposure to the air into another iron tannate, which is insoluble and constitutes the black pigment of writing.
Characters written with a pure freshly-prepared iron gall ink are very faint in colour when first applied to the paper, and it is only after the air has acted upon them that they gradually become dark blue and finally black.
In the old type of iron-gall ink, that which was universally employed down to the early part of last century, inks were exposed to the air or were boiled in order that the insoluble black pigment might form within the liquid, and thus give some colour to the ink when it was first put upon paper. The objection to this is that ink thus prepared is liable to clog the pen and not to penetrate properly into the fibres of the paper.
In the modern type of inks, therefore, which are commonly known as “blue-black” inks, this method of partial oxidation is not employed, but a colouring matter is added instead, so that the writing has some colour immediately, pending the formation of the black pigment within the fibres of the paper.