19. (Dr Ure.) Galls, 12 lbs.; green copperas and gum Senegal, of each 5 lbs.; as No. 2 (nearly). To produce 12 galls.
20. (Dr Wollaston.) Galls, 1 oz.; sulphate of iron, 3 dr.; gum, 1⁄4 oz.; cold water 1⁄2 pint; put into a bottle and shaken together every day for a fortnight or longer. A good durable ink, which will bear diluting.
21. (Pharmaceutische Zeitung.) By adding ferrocyanide of potassium to ordinary ink, an indelible writing ink may be obtained. The removal of such an ink by an acid would result in the production of Prussian blue.
General Commentary. According to the most accurate experiments on the preparation of black ink, it appears that the quantity of sulphate of iron should not exceed 1⁄3rd part of that of the galls, by which an excess of astringent vegetable matter, which is necessary for the durability of the colour, is preserved in the liquid. Gum, by shielding the writing from the action of the air, tends to preserve the colour; but if much is employed, the ink flows languidly from quill pens, and scarcely at all from steel pens. The latter require a very limpid ink. The addition of sugar (especially of moist sugar) increases the flowing property of the liquid, but makes it dry more slowly, and frequently to pass into an acetous state, in which condition it acts injuriously on the pen. Vinegar, for a like reason, is not calculated for the menstruum, as it rapidly softens quill or horn, and corrodes iron and steel.
To ensure the permanency of the colour of the tanno-gallic inks, the best Aleppo or blue nut-galls must alone be used. No second or inferior quality should be employed. A contrary practice, often adopted for the sake of economy, is nearly always followed by unpleasant results and often by considerable loss.
The only improvement of importance which has been made in the manufacture of writing ink from the common materials, during the last few years, is the practice of first roasting the gall-nuts, which is now adopted by a few of the houses most celebrated for their COPYING INK. In this way a portion of pyrogallic acid is formed, which is very soluble in water, and strikes an intense bluish-black colour with the protosulphate or green sulphate of iron. From galls so treated an ink may be made to write black at once. Care must, however, be taken to avoid any loss of materials by volatilisation.
To prevent any tendency to mouldiness in ink, a few bruised cloves, or a little oil of cloves, or, still better, a few drops of creasote (carbolic acid) may be added. The last two should be previously dissolved in a small quantity of strong vinegar, or rectified spirit. With the same intention some of the large makers allow the ink to become covered with a skin of ‘mould’ in the cask, to render it less liable to undergo the same change when subsequently bottled. Formerly the practice was to add a little spirit for the same purpose.
Sumach, logwood, and oak-bark are frequently substituted for galls in the preparation of common ink. When such is the case, only about 1⁄6 or 1⁄7th of their weight of copperas should be employed. Inks so made possess little durability.
The very general use of steel pens of late years has caused a corresponding demand for easy-flowing inks, many of which are now vended under the titles of WRITING-FLUIDS, STEEL-PEN INK, ANTICORROSIVE INK, &c. The greater number of these are prepared from galls in the preceding manner; but a less quantity of gum is employed, and greater attention is paid than heretofore to avoid every source of ‘greasiness’ among which smoke and dirty utensils are, perhaps, the principal. The blue ‘writing fluids,’ which either maintain their colour or turn black by exposure to the air, are, in general, prepared from ferrocyanide of potassium, or from indigo, and are fully noticed in another place. Copying ink, another variety of ink of recent introduction, is characterised by its suitableness to metallic pens, and by furnishing a transcript by means of the ‘copying press’ or ‘copying machine.’ (See below.)
The inks prepared by the first four of the above formulæ are very durable and limpid, and will bear dilution with nearly an equal bulk of water, and still be superior in quality to the ordinary inks of the shops. See Galls, Iron, Writing fluid, and below.