История письма и чтения. Асафова Г.К. - 133 стр.

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kerosene, in which case drying takes place by evaporation. The colouring

ingredients come in several forms: pigments, which are fine, solid particles

manufactured from chemicals, generally insoluble in water and only slightly

soluble in solvents; agents made from chemicals but soluble both in water and in

solvents; and lacquers, obtained by fixing a colouring agent on powdered

aluminum. The additives stabilize the mixture and give the ink additional desirable

characteristics. The nature and proportions of the ingredients vary according to the

printing process to be used and to the material to be printed. The proportions must

be checked and sometimes modified during printing.

Letterpress and offset use greasy inks. For printing on sheet-fed presses,

thick greasy inks are used in which the vehicle is generally made of vegetable oils

with the addition of hard natural or synthetic resins dispersed in mineral oils. Roll-

fed rotaries use fluid greasy inks in which the vehicle is made up of heavy mineral

oils.

The colour black is generally obtained from an organic pigment, carbon

black, derived from the incomplete combustion of oils or of natural gas. Coloured

pigments are inorganic compounds of chromium (yellow, green, and orange),

molybdenum (orange), cadmium (red and yellow), and iron (blue).

Inks for offset are more highly coloured than those used in letterpress,

because they must be transferred to the blanket before they reach the paper.

Furthermore, the pigments must resist being picked up by the water from the

dampening system.

Inks with various special qualities exist for both letterpress and offset. In

high-gloss inks, the vehicle is not homogeneous, as with ordinary inks, but

heterogeneous, based on synthetic resins dissolved in a solvent, with lead and

cobalt additives. This ink glazes as it dries. When printing several colours, the

whole series of operations must be finished before the ink has time to dry so that

the inks can attach themselves to the surface.

Quick-setting inks utilize a vehicle that also has a base of resins dissolved in

a quick-drying solvent.