y have had
no experience on rotary presses. All these difficulties are sure to be
overcome in time.

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 ag