Part 17 (1/2)

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.