Ink

Printing ink, as everyone must be aware, is a very different composition to that used for writing. It is a soft, glossy compound, having a certain amount of adhesiveness, and becoming, by exposure in thin layers, perfectly bard and firm. Besides these properties, which always belong to it, it possesses and various attributes, according to the numerous purposes to which it is applied.

Its preparation demands not only a tolerable proportion of scientific knowledge, but also very careful manipulation, and manufacturers have found that to produce it of good quality both experience and deep study are requisite. The very important use for which it is designed—the in a permanent form the productions of the mind—indicates some of the properties it ought to possess. The most valuable of these is durability, or the capacity to resist successfully the obliterating influences of time, and it should also have brightness and depth of tint. It must be a mutable preparation, passing from the soft, adhesive state to that of a perfectly hard and dry substance, and this change of condition must have a certain rate of progress, and be, to some extent, under control. When prepared, some time generally elapses before it is used, and during this period it should not alter in the slightest degree; in fact, when the air is excluded from it it should keep for almost any length of time.

During its application to the type, its solidification should be as slow as possible, and unaccompanied by the emission of any unpleasant or deleterious odour. It ought not to effect the soft elastic rollers which are employed to convey it to the type, and which, unless the ink be a perfectly harmless preparation, are liable to considerable injury. The change of state should not he accompanied by the doposition of consolidated mailer in the ink, as this impedes the pressman and proves a loss to the printer. Printing ink should, moreover, have an oleaginous character; it ought to be very glossy, and perfectly free from any granular appearance. If, on the extraction of a small portion from a mass, it leaves but a short thread suspended, it is, considered good, but the best test of its consistency is the adhesion it shows upon pressing the finger against a quantity of it.

The requirements of a good printing ink do not end here. Having been applied, its action must be confined to a very slight penetration into the paper—just sufficient to prevent its detachment without materially injuring the surface of the latter. It ought to dry up in a very short space of time to a hard inodorous unalterable solid.

The ingredients of ordinary printing ink are burnt linseed oil, resin, and occasionally soap, with various colouring matters. The best quality of linseed oil is used, and this is purified by digesting it in partially-diluted sulphuric acid for some hours, at a temperature of about two hundred and twelve degrees, allowing the impurities to subside, and then washing away the acid with repeated additions of hot water. The oil, alter this treatment, is pale and turbid, and if the freeing from the acidis complete, there is scarcely any odour. By rest, the oil clarifies, and has then a pale lemon colour. It now dries much more rapidly than before. The purified oil is now partially resinified by heat. For this purpose it is introduced into large cast-iron pots, and boiled until inflamable vapours are freely evolved. These are ignited and allowed to bum for a few minutes, after which they are extinguished by placing a tight cover over the boiler. Ebullition of the oil is continued until, on cooling, a firm skin forms on its surface, known by placing a drop on slate or other smooth, cold surface.

Other drying oils besides linseed are occasionally used, but their cost, or other considerations, prevents their general adoption. Resin oil, is, indeed, pretty largely employed, but apart from other disadvantages, its disagreeable and permanent smell prevents its entering into other ink than that intended for temporary or common printing, as newspapers, posters, &c. Paraffin oil, which has lately been used, is open to the same objections. Resin is an article of considerable importance in the manufacture of printing ink, since, when dissolved in the oil—after the latter has undergone ebullition and inflammation—it communicates body to the fluid. For many inks the quality of the common black resin is sufficiently good, but some require the pale, clear, transparent resin, obtained by re-melting and clarifying the residue of the distillation of turpentine with water.

The colouring matters of printing ink demand great attention, as much of the beauty of typography depends upon them. The universal ingredient for black ink is lamp black. No expense is spared to get the most superior qualities. Other black substances are occasionally used. Charcoal trom various substances, when reduced to an impalpable powder, and mixed with other ingredients, furnishes a deep, blue-black ink that dries rapidly. The brown tint possessed by lamp-black is not unfrequently neutralised by the addition of blue compounds, as indigo, Prussian blue, &c. The various colouring matters employed in the preparation of other inks are all selected for their superior and approximate qualities.

Indeed, the manufacture of printing ink is an especial business and demands considerable capital. Every manufacturer has his own secrets, both as to material and process, and by long experience alone can printing ink manufacturers so select and apportion the numerous ingredients as to adapt it to its numerous requirements. In the manufacture of printing ink, the resin is dissolved in the burnt oil, in cast-iron pots or boilers, and the varnish, thus prepared, is introduced into what is termed the “mixing vessel.” which is cylindrical, and in the centre of which bars, or rods of iron, attached to a perpendicular shaft, revolves in a horizontal position. The colouring matter is then added to the hot varnish, and the whole, when thoroughly mixed, is drawn off through an opening in the base of the vessel. The pulp is next very carefully ground, by being passed between hard stones of a very tine texture, driven by heavy machinery, the motive power being steam. Sometimes a second grinding is requisite, but this may generally be avoided, by taking care that the varnish of resin and oil is clear and free from gritty particles, and that the black is in an impalpable state.

The proportions and conditions of the various ingredients vary considerably, and great experience is required before an ink can be prepared to suit any one purpose. The oil has to be rendered more viscid, by burning, in some cases than in others; sometimes the quantity or kind of resin requires to be varied; or, perhaps, different proportions of colour are requsite. Newspapers printed on machines require an ink of less substance than that employed for book-work, which must be tolerably stiff. For wood-cuts, the ink must not only be very stiff, but very fine. The qualities of the material to which the ink is applied furnish an additional guide in this matter—thin paper must have a soft ink, which works clearly and is not too adhesive. A fine, stout paper, on the other hand, will bear a stiller and more glutinous ink, and as resin supplies these properties, so does it, in a great measure, communicate brilliancy, and the most perfect and splendid effects are by these means produced. Posters, with large wood type, require a semi-fluid ink, but one not surcharged with oil. Ordinary news-work requires a better quality, more “tacky” and finely ground. Good book-work should have a stiller bodied ink, soft, smooth, and easily distributed. Job ink, which is made expressly for press-work on dry paper, should be used only for such work. Hook and job inks are not convertible; an ink for wet paper will not work well on dry paper, and vice versâ. Very fine presswork, such as woodcuts, or letterpress upon enamelled paper, requires an ink impalpably fine, of brilliant colour, of strong body, yet soft enough to be taken up smoothly on the inking rollers. Every general printing office should keep lour grades of ink—News, Jobbing, Book, and Woodcut. Fine presswork is impossible withoul good ink.

To recapitulate: the cardinal virtues of good ink are, intenseness of colour; impalpability; covering the surface perfectly; quitting the surface of the type or engraving when the paper is withdrawn, and adhering to the surface of the paper; not smearing after it is printed; and retaining ever afterwards its original colour without change. Inks which are properly manufactured on sound chemical principles, should possess the additional advantages of keeping the roller in good working order, distributing freely, working sharp and clean, and drying rapidly on paper; the colour should be permanent, without a tendency to turn brown by age.

The price of printing inks has undergone some remarkable modifications of late years. In a price list contained in Stower’s “Printers’ Grammar,” published in 1808, the very cheapest quality is quoted at 16d. per ℔.; very good useful ink is now largely supplied at less than 6d.—See Dry Colours, and Printing in Colours.