The process of making printing ink consists of grinding a pigment, black, white, or colored, into a suitable varnish. The pigment is that constituent which makes the impression visible, while the varnish is the vehicle which carries the pigment during the operation of grinding and during its distribution on the press to the type, from the type to the paper, and ultimately binds it to the paper.

A complete factory for the production of printing ink consequently consists of three distinct plants,—one for the production of the varnishes, one for the manufacture of the pigments, and one for the grinding of the pigments into the varnishes.

Roughly speaking, the varnishes are divided into three classes, the first and second of which are the varnishes proper, i.e. the resin and the linseed varnishes, while the third class consists of dryers, etc., whose purpose is to influence the drying and consistency of the inks.

Taking up first the proper varnishes, we find that these are produced by the destructive distillation of resin in huge cast-iron stills. By this process, the solid resin of colophony is split up into water, various resinic acids or naphthas, and resin oils of various specific gravities and consistencies, all of which are separated from each other into separate containers which are ready to receive them. As one distillation is not sufficient to purify the resin oils from the water and acid, which would not only give the resulting ink an obnoxious odor but be detrimental to type, plates, etc., the distillation is repeated a number of times until the oils become perfectly pure. The grades of varnishes made from these resin oils are used for the cheaper classes of printing inks, not only on account of their lower cost, but because they are more suitable for the class of work for which such inks are used.

The linseed varnishes are made by boiling refined linseed oils at a very high temperature. The linseed oil loses its acrid elements by volatilization, and gradually becomes thick and viscous, the various "numbers" or consistencies of these varnishes being dependent upon the length of time during which the oil is subjected to the process, and to the temperature applied.

The dryers are made by adding to the linseed oil during the boiling, suitable oxidizing agents, such as compounds of lead or manganese, by means of which the oil is chemically affected, i.e. it is oxidized. Such dryers, when added to printing ink, attracts the oxygen of the air and transfer it by catalytic action to the varnish of the ink, thus causing it to oxidize more rapidly, or to become, as it is commonly called, dry.

Having disposed of the manufacture of the varnishes and dryers, we now come to the manufacture of pigments. This is such a large field that it can be only cursorily covered within the limits of a short article. The pigments are of many kinds and classes. The blacks alone would form a large chapter by themselves; yet all of them consist of carbon, produced by the combustion of hydrocarbons of various kinds, and according to their origin they are the so-called carbon blacks, lamp blacks, spirit blacks, oil blacks, Frankfort blacks, etc., each of which has its distinct and peculiar properties and value for its specific purpose.

The other pigments fall naturally into two divisions,—chemical colors and the so-called "lakes." The chemical colors are in general of mineral origin, produced by the action of one chemical upon the other, or in some cases by physical or chemical action upon earths and ores. In the first group, we have such colors as vermilions, white lead, chrome yellows, the ferrocyanide blues (Milori blues, bronze blues, Prussian blues, Chinese blues, Antwerp blues, Paris blues, Berlin blues), ultramarines, etc.; in the second group, such colors as cyanides, umbers, Indian red, and many others.The lakes are principally formed by the use of coal-tar derivatives, and are usually incorrectly grouped as anilines. They are produced by precipitating water-soluble dyes upon a suitable substratum or base. Their shades, strength, brilliancy, permanency, and working qualities are dependent upon the nature of the dye itself, upon the nature and percentage of the substratum or base, and also upon the suitable selection and manipulation of the precipitating agents. This class of colors is to-day by far the most important of all, since through great progress made in chemistry in recent years, it is possible to make them of the greatest possible strength and permanency, together with a brilliancy of shade which was for many years an ideal earnestly striven for, but apparently impossible to accomplish.

Having thus considered the products which are the principal raw materials of printing ink, we now come to the ink itself. Being provided with all the varnishes, pigments, dryers, etc., of suitable qualities and shades, it is necessary to combine them in proper proportions, after selecting such as will be mutually compatible, and to grind them to the utmost fineness. The machinery to accomplish this purpose consists, first, of mixers, in which the ingredients are thoroughly incorporated with each other. This being done, the resulting mixture or "pulp," as it is called, is ground upon mills formed of rollers or cylinders, which are set in close contact by means of screws and made to revolve by power. Between these rollers the pulp is passed again and again, the number of times being dependent upon the consistency of the ink and the nature of the pigments, until it is ground or comminuted to the utmost fineness. The result is printing ink as it is known to the printer, varying in consistency, strength, intensity, permanency, brilliancy, drying, and other working qualities, according to the nature of the various varnishes, dryers, and pigments with which it is made.[Back to Contents]