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.
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.