Just as the second stage has, particularly for book-work, virtually superseded the first, so the third is destined to supersede the second. It is only an adaptation of the means to the ends. The mechanical principles of the rotary press are, in fact, simpler than those of the flat-bed cylinder press, and it may be said that so far as the purely mechanical part of the press is concerned, they have been fully developed, but much still remains to be done in other directions. The variety in the sizes of the pages of different books, the smallness of the editions, and the fact that the finer grades of paper, especially coated paper, cannot be obtained in roll form, are obstacles to be removed. As most book forms are electrotyped for flat-bed presses, and as it requires but little additional expense to curve the plates, this one item is not much of an obstacle to overcome. It is, however, still difficult to curve the plates perfectly, and the pressmen, even if they can produce excellent work from flat-bed presses, require considerable training if they have had no experience on rotary presses. All these difficulties are sure to be overcome in time.[Back to Contents]
PRINTING INK
By James A. Ullman
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.