Scientific American 19, 21.1.1854
(Abstract of a Lecture on the "Chemistry of Writing Fluids," delivered before Bacon's Cincinnati Mercantile College, by Prof. Chas. W. Wright, and reported expressly for the Scientific American.)
Intensity, fluidity, permanence of color, and absence of corrosive properties, are the desirable qualities in a writing fluid, and can only be accomplished by proper manifestations and a strict attention to the purity of the ingredients and in its preparation.
Black Ink is the medium commonly used for the purpose of expressing thoughts and words permanently upon plane surfaces,a s paper, parchment, &c., and is the one that we shall first consider in a chemical point of view.
The bases of black inks are the two salts of iron, known to chemists as the tannate of iron, and the gallate of iron, both of which are invariably found in black ink which contains vegetable astringents, as nut-galls, oak bark, &c. The iron salt should be wholly, or in parts peroxidized, as the proto salts of that metal have no colorizing effect upon tannic and gallic acids the best being a mixture of the protosulphate and persulphate of iron, which can be obtained by exposing green vitriol or copperas to the atmosphere for some time.
If the iron be in the condition of a per salt the ink is intensely black when first written with, but does not retain its depth of color and is easily erased from paper. This is the case with the Japan ink which is made of copperas that has been highly peroxidized by roasting. When the proto and persulphate of iron are both employed in the preparation of ink, it is not of a deep black color when first written with, but speedily becomes so on exposure to the atmosphere, and this is the condition of the iron to be preferred as it is partly in solution and sinks into the substance of the paper, and is removed with difficulty. Ink prepared from nut galls, oak bark, and some other astringents is, when first made, of a bluish black color, while that in which catechu, kino, or green tea are used has a greenish tinge when first written with. Arnold's writing fluid which has such an extensive sale in this country, can be imitated by employeing iron in the state of the protosulphate in place of a mixture of the two sulphates and coloring the solution with sulphate of indigo or soluble Prussian blue, and if a greenish tinge be desirable, it can be given by the addition of some yellow coloring matter to the solution of Prussian blue, or indigo. Ink prepared in this manner, soon loses its blue or greenish color, when the writing is exposed to the air, and, when well made, forms a beautiful flowing black ink.
Sugar and gum are used for thickening writing fluids and it is a little singular that two substances should be accidentally selected for this purpose that are identical in chemical composition, sugar and starch each having twelve equivalents of carbon, and hydrogen and oxygen in the proportion to form water, thus C.12 H.11, O11.
When sugar is used, the ink flows more easily from the pen, but is liable to be transformed into vinegar, which will corrode steel-pens. Gum is not so liable to become sour, and has the additional advantage of forming a varnish as it were, over the surface of the writing when it becomes dry, and in this manner renders it less liable to be removed by mechanical means. Great care must be exercised in the use of gum, particularly when steel-pens are in use, as they require an easy flowin ink, and too great a quantity of that substance will render it thick and totally unfit for writing with.
Mouldiness is counteracted by the addition of a small quantity of the oil of cloves, creosote, or corrosive sublimate, the latter in small amount is probably more efficient than all others but it should be remembered that it is a deadly poison.
All inks containing tannic or gallic acids, can be bleached or removed by means of oxalic, citric, or phosphoric acids, or by any of the bleaching salts of chlorine; and ink-stains and iron mould can be removed in the same manner. faded writing can be restored by the use of a decoction of galls, or a muriatic acidulated solution of the yellow prussiate of potash.
Blue Ink is generally made by dissolving sulphate of indigo, or basic Prussian blue in water and thickening the solution with a little gum. Common Prussian blue is rendered soluble in water by the addition of muriatic or oxalic acids. Booth and Morfit give the following recipe for making soluble Prussian blue. "Dissolve in a solution of iodide of potassium, as much more iodine as it contains, and pour this solution into one of yellow prussiateof potash containing as much of the solid prussiate, as the whole amount of iodine. Soluble Prussian blue precipitates and iodide of potassium remains in solution. After filtering, the precipitate is dissolved in water, and forms a blue ink containing no free acid and therefore adapted to steelpens. If the soluble blue be added to common black ink, (from galls), the result is a black ink which cannot be removed from paper without destroying it."
The next lecture will be devoted to indelible inks and paper.