Part 17 (2/2)

Sometimes it is necessary to turn the dampened paper in order to remove the creases. Separate the sheets into two piles and lay a few sheets from one to the other so that the altered positions will press the sheets flat again.

With many papers, especially the unsized, it is possible to use the method of book-printers, who immerse a whole book in water and then lay the sheets in two equal parts. This would be best studied at a printer's. It requires much practice.

If dampened paper is permitted to lie some hours without being weighted down, the margins will become too dry, and then there will be creases during printing, which can be remedied only by a second dampening. The reason is that dry paper is not so large as wet paper, so that the dry margins form a kind of frame which is too small for the inner wet portion.

In printing-processes that require many plates, and especially if the sheets are large, only dry paper can be used, as otherwise the register will be imperfect. To be sure, it can be done by using great care, but too much practice and attentiveness is needed.

With the exception of the aquatint processes, good printing can be done with dry but unsized paper. But the press must have twice or thrice the pressure. This makes the printing more difficult and endangers the stone if it is not thick.

CHAPTER VI

PRESSES

An exact description of all presses used hitherto for lithography would demand a book that would nearly equal the present one in magnitude. Many drawings would be necessary, which would increase the cost of this text-book without adequate benefit, as I have learned that one rarely can find a mechanician skillful enough to make a machine even when he has the very best description and a perfect ill.u.s.tration before him. I advise all who intend to enter lithography to send for a model to Munich or some other place where the art is being practiced with success. I myself am willing to furnish exact models for the price of one louis d'or, which must be remitted with the order.

There is no press as yet that is so perfect for lithography that it leaves nothing to be desired. The press whose plan I laid before the Royal Academy of Sciences in Bavaria, which does its own inking-in and which can be worked by water-power, has not yet been built on a large scale, so that its value cannot be stated exactly.

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 sc.r.a.per. 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 sc.r.a.per 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 sc.r.a.per.

As the sc.r.a.per must be pressed down with great force (often as much as sixty and more hundredweight) and must pa.s.s 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 sc.r.a.per. 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 sc.r.a.per. 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 s.p.a.ce between the dots, are so affected by the slightest displacement that they produce a smeared, sooty impression.

The sc.r.a.per has a second fault. If the paper has impurities, it injures the sc.r.a.per readily. A groove scratched into the sc.r.a.per will prevent any further good impression if the injury is considerable, because it will leave a streak. The only remedy is to take the sc.r.a.per off and plane it, fas.h.i.+oning it accurately to the surface of the stone. I have tried to remedy this by making a sc.r.a.per of metal. As this causes even more friction than wood, I laid a strip of strong paper over the sc.r.a.per, 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 sc.r.a.per and six inches wide was available for some thousands of impressions. The pressure attained with a metal sc.r.a.per 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 sc.r.a.per can be planed to suit any irregularity in the stone.

The foregoing shows that a good lithographic press must have these two properties:--

(1) It must not pull or s.h.i.+ft the paper in the least.

(2) It must produce a uniform impression without weak spots or streaks.

The other properties it needs in common with other presses, such as:--

(3) It must be powerful enough to produce the necessary pressure.

<script>