The Invention of Lithography Part 17

Usually the paper considered most excellent for copper-plate work is thick, tender, uniform paper, half-sized or not sized at all. It may be the same for lithography. However, it must not be supposed that good impressions cannot be obtained with sized paper. I have seen some that were as good as, and even better than, impressions made at the same time on unsized paper. Much depends on the dampening of the paper, on its make, and chiefly on the manner of sizing it. On the best sized English vellum paper, I have made blacker impressions than I could make on the best Swiss copper-plate printing-paper, so that I had to use fifty per cent less printing-color. On the contrary, in using an indubitably genuine English vellum paper with a bluish tinge, which had been sized only too well, I could not get good impressions despite all efforts. It was very hard to dampen also. Every sheet must be dampened singly, turned frequently and manipulated to smooth out the thousand irregularities that are caused by the moisture. Equally difficult to use were some sorts of genuine Holland paper, because they took color reluctantly. If, however, the correct degree of moisture is attained, if the paper takes it well, and, finally, if the color is right for it, it can be used with thorough success.

I must mention a circ.u.mstance that may defeat all efforts of a beginner should he try to use a certain kind of paper which is very handsome, durable, very white, well sized, but a little rough and possessing an odor somewhat resembling honey as well as urine. Sometimes it is called _Kuhnel_, and comes from a French factory. This paper has the property of depriving the stone of its preparation, and consequently to s.m.u.t it.

This paper can be used only for dry printing, where it does not require any dampening at all.

It is said that this property of s.m.u.tting the stone is due to the chemical bleaching. Others ascribe it to a peculiar kind of size.

Perhaps it is both. The same defect is found in many sorts of colored papers if there is much alum in the coloring-matter, or if the tints are made from alkaline colors or those that contain soapy matter, or if it has been smoothed with soap. This, however, is readily understood after my explanation of the chemistry of the stone.

IV

DAMPENING THE PAPER

Dry paper may be used for printing. In certain work it is necessary, in order not to spoil the paper. As a rule, however, paper is moistened in lithography as well as in other forms of printing, to make it softer and more receptive to the printing-color.

After what I have said of chemical printing, it would seem that, as dampness is antagonistic to the reception of color, the moisture of the paper would hinder, rather than aid, printing. But experience proves the opposite. A damp paper takes color better than a dry one.

But this is not because damp paper is an exception to the rule. On close study, we see that here, too, it only proves all that I said about the stone.

Perfectly clean, and especially unsized paper, refuses color like the prepared stone, when it has been wetted thoroughly so that it is saturated. But here, too, mere water is not a complete preparation.

Under strong pressure it is forced away readily from the paper, the printed places are dried and the color adheres. If the pressure is not sufficient to force all the water away, the impression will be imperfect. The tougher the printing-color is, the more will it resist the dampness and the greater must be the pressure.

Experience has taught me the following:--

(1) Every paper not spoiled with fat will permit itself to be prepared, like the stone, with water so that it will take no color. In the case of entirely clean, unsized paper, water alone is sufficient. Mucous, gummy, and acid substances increase its power. Unsized printed paper need merely be dipped in water, laid on a stone, and coated with oily color, and the printed parts will all take the color while the rest of the paper remains white.

(2) Any great pressure will remove this preparation and the whole paper will take color.

(3) The oil color must be very thin and fluid, because a tougher one will take hold of the fibres of the paper and tear them off.

The foregoing experiences applied to the theory of the print itself lead to the following conclusions:--

(_a_) The paper to be used for printing must never be too wet, because the most powerful pressure could not remove the water sufficiently.

(_b_) Paper that is too wet is p.r.o.ne to adhere to the stone with its printed parts, which are likely then to tear away easily, thus damaging or ruining the work. This happens the more readily if the pressure be not sufficient. If the sc.r.a.per or the stone is not uniform and even, it is very p.r.o.ne indeed to tear at the places subjected to the least pressure, because there, where the water has not been sufficiently squeezed away, the paper remains soft and fragile, while the pressure still is great enough to grip the fibres of the paper.

(_c_) Therefore the paper must be only slightly dampened if the color is very tough, partly to prevent tearing, partly to oppose no undue obstacle to the reception of the color.

(_d_) Paper dampened too much stretches in printing and produces uneven and dirty impressions.

(_e_) The quality of the water is not important so long as it is not dirty or putrid, in which latter case it may infect the paper and rot it.

(_f_) Just how much the paper must be dampened can be learned only from experience, because papers vary very much and in the case of sized papers it depends chiefly on the kind of sizing. On the average, we may calculate one wet sheet to eight dry ones in sized papers and one wet one to ten or twelve dry ones in unsized papers.

The following is the best way to dampen paper: Lay two or three dry sheets on a straight board. Then dip a sheet into water. Let the water drip off a little and lay the damp sheet carefully on the others. Now lay eight or ten dry sheets on top of this. Then put on another wet one and then eight or ten dry ones and so on till all the sheets destined for printing have been so piled up. Put over all a board weighted with a medium heavy stone plate. After half an hour increase the weight to several hundredweight or squeeze the paper in a press. Leave it thus at least twelve hours. Then it is generally ready for print. In aquatint it must be dampened more, about six dry sheets coming to one wet one.

Very thoroughly sized paper is easier to moisten if each sheet, or at least each second one, is wetted with a sponge.

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.