Another feature upon which colour sequence in printing largely depends is the point at which the outline forme can be most effectively introduced. It is advisable to print the outline forme at as early a stage as possible for obvious reasons. Perfect registration is far from easy to secure. Red in the lips, blues in the eyes, and isolated touches of colour in various parts of the design must fit the browns, and therefore fit each other, and yet they may have no direct relation to each other in the printing. A remedy has been already suggested, but once an outline forme is printed the cause of bad registration is to some extent removed, and a remedy quite unnecessary. When worked on reasonable lines it is frequently an advantage to make the outline one of the earlier printings, so that any harshness of contour, etc., may be toned down by the succeeding greys. It is often a matter of personal opinion, or perhaps of circumstance, which decides the final printings. The pink may be reserved to impart brilliancy and warmth to the prints, or it may be equally suitable to hold back a grey, and, by regulating its tone and strength, soften down any tendency to hardness, pick out the darker prints, and emphasise the shadows. Even these suggestions, although usually regarded as standard ideas, must be subjected to modifications under certain conditions.
Here is a practical instance. Unless paper is unusually well seasoned and of first-rate quality, the temperature of the workroom equable, and the printing machine in good order—a combination of excellences which is unfortunately rarely met with—the colour sequence must be of a fairly elastic nature. To print a gold first is quite usual, because the bronze powder will persistently adhere to any preceding printings. From that standpoint alone such a procedure would be eminently practical and convenient, but suppose for a moment that the gold must fit a later printing with absolute accuracy, e.g. an outline forme, or as forming the base for some ornamental scheme, then the difficulties which arise are somewhat trying, and for this reason. The paper being new, the most serious distortion of any kind is likely to occur during the first printings, and so long as yellows, fleshes, or other colours of a similar character are printed first, no serious difficulty is likely to arise; but with the gold printing it may be altogether different. It is quite possible to make both yellow and flesh dry dead, i.e. without even sufficient tack to catch the almost impalpable bronze powder. At the same time, care must be exercised that the colouring matter is not left dry on the surface of the paper owing to its separation from the reducing medium. This plan has been adopted under actual commercial conditions and with conspicuous success, and it is therefore offered as a preventive measure which is free from many drawbacks which are the frequent accompaniment of novel ideas and operations. Here then is a simple practical summary of the idea. The yellow and flesh, or equivalent colours, are printed first, so that they will dry free from gloss or tack. The fit required between such colours and subsequent printings is generally a matter of minor importance, and at this stage distortion of the paper, whether it be by stretching or contracting, will not seriously depreciate the value of the print when completed. Register between the gold and an outline is frequently of an entirely different character, and in many cases the slightest variation will be readily discernible, and have a decidedly bad effect on the finished work. Apart from this, the questions which decide or control the colour sequence have been clearly indicated previously.
This matter may be one of convenience also, for unless otherwise predetermined it would be unwise and far from economical to print a blue before a yellow, or a black before a red, etc. The amount of cleaning up thereby involved would become a serious and distinctly disagreeable item, and purity of tone in the lighter colours would be conspicuous by its absence.
The matter of well seasoned printing paper has been already referred to. For effective colour printing the paper must also possess several other essential qualities. It should be firm in substance, sufficiently absorbent to carry the successive layers of printing ink, as far as possible unstretchable, and should present a smooth surface though not a glazed one. The chalky, dull, enamelled papers offer many recognised features of value to the colour printer. They assist in the absorption of the ink as well as afford a suitable surface for their impression. Friction-glazed and other prepared papers are also excellent for colour printing by lithographic methods.
CHAPTER X
Lithographic Colour Printing—continued
Printing Inks—Varnish—Reducing Medium—Relative Values—Some useful Hints—Bronze Blue—Vermilion—Ink Mixing—Ceramic Transfers—Colour Transparencies.
For the successful manipulation of printing inks of any description it will be necessary to know something of their composition, or at any rate of such features as render them peculiarly suitable for printing purposes. From a printer’s point of view the most important of these features is what may be described as the reducing medium, i.e. the medium which holds together the various colours so as to produce pigments of suitable working consistency. The most useful and the commonest form of reducing medium is a linseed oil product, known in its prepared state as a lithographic varnish, with a supplementary title indicating its specific character. Its value to the lithographic printer lies mainly in the fact that when it is fully matured it possesses a good full body along with fair drying properties and freedom from any excess of greasy matter. This varnish is used in three or four consistencies between which any degree of strength may be arranged by mixing. A brief outline of the manner in which they are prepared may still further emphasise their usefulness in lithographic printing.