I am only too well aware, however, of a grave defect in lithography, which is that the beauty and even the number of impressions depend mainly on the skill and the industry of the printers. A good press is necessary, to be sure; but even with the best a poor workman will produce nothing but trash, because in this respect lithography is far more difficult than any other printing-process. I shall not admit that lithography has made a great step toward the utmost perfection until the erring work of the human hand has been dispensed with as much as possible and the printing is done almost entirely by machinery. Therefore I am determined to realize the ideas I have in this direction and I shall inform the friends of the art of my success at once.
I
PROPERTIES OF A GOOD PRESS
It has been observed that inscriptions, and particularly drawings, look better on the stone than on the impression afterward made from the stone. Partly this may be due to the color of the stone which softens the picture, because an impression made on yellow paper resembling the stone color looks very much like the drawing on the stone. But the great cause of the difference is that the color does not transfer itself to the paper with the degree of strength and clearness that it possesses on the stone. That this perfect degree can be attained, none the less, there are many successful impressions to prove.
If the plate is well designed and well prepared, it will take the color well and clearly, but the printer may apply too much or too little, the color may be too hard or too soft, or, even if the stone is properly inked, the paper may accept color poorly or be too damp or dry. Chiefly, however, it is the press, according to my experience, that most affects the quality of an impression.
In most lithographic presses the printing is done by the so-called scraper. This is a thin slat of hard wood, mostly maple, pear, or boxwood. It is one line thick on the side intended to do the printing, and the mechanism of the press forces it on the paper, which is on the stone and covered with an overlay of waste paper and tensely stretched leather. This pressure forces the color against the paper along the whole length of the slat, and only one line broad. The scraper is forced bit by bit over the entire plate, or it remains motionless and the plate is drawn underneath it.
It will be observed that this kind of press does not produce the entire impression vertically and at once as in book-printing, but that it is successive, as in copper-plate printing, with the difference that the copper-plate press uses a roller instead of a scraper.
As the scraper must be pressed down with great force (often as much as sixty and more hundredweight) and must pass over the leather with this immense pressure, there is a tremendous friction, and despite the fact that the leather is tensely stretched and lubricated with fat, it is considerably pulled and strained by the scraper. This pulling and straining communicates itself to the paper under the leather. Thus all the lines of the design become a little bit squashed in the direction described by the scraper. If, however, the leather is very good and very tensely stretched in the frame, if it is well lubricated, and if the printing-paper with its underlay is not too wet, the pulling is inconsiderable so that scripts and drawings in broad effects are not affected noticeably. Drawings in detail, however, and crayon work wherein there is hardly a perceptible space between the dots, are so affected by the slightest displacement that they produce a smeared, sooty impression.
The scraper has a second fault. If the paper has impurities, it injures the scraper readily. A groove scratched into the scraper will prevent any further good impression if the injury is considerable, because it will leave a streak. The only remedy is to take the scraper off and plane it, fashioning it accurately to the surface of the stone. I have tried to remedy this by making a scraper of metal. As this causes even more friction than wood, I laid a strip of strong paper over the scraper, which generally was good for three hundred impressions before it was worn out. Then I merely needed to move it forward a bit; so that a strip of paper as long as the scraper and six inches wide was available for some thousands of impressions. The pressure attained with a metal scraper is greater than with wood; but it has the disadvantage that it is hard to print a stone whose surface is not absolutely level, whereas a wooden scraper can be planed to suit any irregularity in the stone.
The foregoing shows that a good lithographic press must have these two properties:—