Three kinds of paper are used mainly in lithography. They are:—
(a) the transparent, oiled or varnished paper;(b) underlay or waste paper; and(c) the printing-paper.
(a) the transparent, oiled or varnished paper;(b) underlay or waste paper; and(c) the printing-paper.
Oiled paper is used for tracing a drawing accurately and then transferring it to the stone either by transferring or by re-tracing it on the stone. It must have the following properties:—
(1) It must not smut the original drawing on which it is laid. Consequently it must be absolutely dry.
(2) It must be very transparent, like glass, so that the underlying drawing or painting can be seen perfectly.
(3) The ink or lead crayon used for copying must lie on it easily and plainly.
It is at its best if it is easy to work on it with a fine brush, using Chinese ink, or, (if the drawing is to be transferred directly to the stone), with the soft chemical ink described under the caption "Transfer Ink." Generally this can be done without further preparation in the case of most papers made transparent by oiling. Varnished paper, however, which is far more transparent, generally must be well washed with milk and dried again beforehand, that it may take the ink well and permit work with the finest strokes.
(4) Finally, a good tracing-paper must be very fine, pliable, tender and yet not in the least brittle. There is some very transparent varnished paper, but it breaks at the first attempt to bend it, so that it is hard to trace the drawing afterward on stone with the tracing-needle, becausenearly every stroke tears the paper and the lines and outlines become coarse.
Very good transparent paper may be made as follows:—
Take the finest writing or vellum paper and soak it with nut or poppy oil, mixed with a little sugar of lead to make it dry more readily. When well soaked with oil, dry it a bit between waste paper and hang it up. Usually it is available in a few days. This paper is cheaper than the paper sold by stationers under the names of straw paper, etc., and about equally transparent. Still more transparent will it be if instead of the oil a varnish cooked from the oils is used. In this also the sugar of lead is an excellent drier. To make the varnish easier to manipulate and more readily penetrative for the paper, it may be thinned down with oil of turpentine. If it is desired to manufacture a greater quantity of this paper, one sheet is laid on another and painted with varnish. Then the whole mass is left for some time covered with a stone plate or a board, that the varnish may soak properly and evenly into all the sheets. Afterward the sheets are hung up singly to dry. The more varnish they have, the more transparent will they be; but too much is not good. Care must be taken that no drops of varnish adhere. It is best to brush the varnish evenly over each sheet before hanging it up.
Silk paper, such as is used in copper-printing to lay between impressions to prevent off-set, is still better for varnishing because it is finer. Only it must be very even and have no holes. The very greatest fineness of paper is desirable, for the reason that then the strokes made by the needle on the stone are fine and not coarse.
Instead of varnish made by boiling down nut or poppy oil, one can use Venetian turpentine, which merely has been thinned down with one half as much oil of turpentine. Such paper generally is dry enough after twenty-four hours. Too large a quantity must not be made at one time, because it becomes tough and brittle after a while.
Even with the most transparent paper it occurs that certain delicate drawings, and especially color pictures, will not show through sufficiently. Then the drawing must be fastened to a window pane to obtain addedillumination. This manner of work is very uncomfortable, however, and the arms hurt one soon, so that it is necessary to stop. It is better to have a tracing-board made with a strong, clear pane of glass in the centre. Under it is a mirror so adjusted that it reflects light upward through the drawing.
It is understood, of course, that in tracing only the outlines are copied and not every stroke of shading, etc. Although the final work is greatly facilitated by the observation of the utmost care in tracing, the tracing of every little detail will merely make the work involved and perplexing. Practice must show the proper degree of exactness. A very good and skillful artist often needs only a few main outlines, to reproduce the original picture with the greatest accuracy.
Once the drawing has been traced sufficiently, the transfer paper must be coated very lightly and evenly with red chalk. Then it is fastened to the stone with wax and all the lines are traced under moderate pressure with a well-polished needle whose point is not sharp but rounded. Where the needle presses the tracing-paper, the color that is on the other side will take hold of the stone and thus transfer the drawing to it. If the needle is too sharp, it will injure the paper, and often the stone and the etching surface. The color on the paper must be rubbed off very carefully with a soft rag. If it is too thick, it will transfer itself coarsely to the stone. The red chalk may be put on the side of the paper that has the drawing on it, or on the reverse. This is decided according as the picture is to be on the stone in the same position as the original or reversed. If the impression is to be like the original, the drawing on the stone must be reversed; therefore in that case the tracing-paper is coated on the same side as the drawing. This side is laid on the stone, and the picture, which shows through, is traced.
In some cases it is good to transfer the drawing from the tracing immediately to the stone without tracing it with the needle. In this case, the paper is not coated with red chalk. The paper is merely laid on the prepared stone, drawing face down, and put through the press. If the drawing has been made with the chemical transfer ink, blackened with lampblackor colored with vermilion according to need, it will transfer itself to the stone. This will occur also in the case of a clean stone prepared for pen drawing if the drawing is made with lead pencil or with red chalk, wet or dry. Even the ordinary ink made from nutgall and vitriol of iron will transfer if it contains a little sugar or gum, but the paper must be well dampened and good pressure must be applied to the press.
In the pen-drawing process, the stone must be cleansed of possible surplus of color after the transfer. This is done by light rubbing with sand. It is not necessary in other processes. Any surplus of color that may have fixed itself to the stone is removed by gentle dusting with a soft brush.
This is used partly for cleansing plates, partly and chiefly as underlay in printing.
If sheets are to be printed on both sides, usually a little of the first impression off-sets on the underlay paper, and if it were used again at once, it would off-set on the next impression. Therefore a fresh underlay paper must be used for each impression of the second side.
This must not be coarse, for fear of causing unevenness or holes in the leather in the printing-frame or in the so-called scraper-wood that makes the impression. A good quantity of this must be on hand, that fresh paper may always be available while the used paper is drying again. Each sheet that has been used should be hung up at once, and not more than three or four sheets should be hung over each other, to facilitate the drying. A special appliance is needed for this as well as for drying the impressions. A number of slats are fastened to the ceiling, leaving a space under it of about two feet, and about one foot distant from each other; and the sheets are hung on these with a pole made for the purpose, such as may be seen in any printery.
Not all kinds of paper are equally good for lithography. On the whole, however, it may be assumed that this form of printing is very similar to copper-printing and book-printing, and that the paper that is good for these branches is suitable also for the stone, if only it does not contain too many impurities, grains of sand and other substances that make any considerable roughnesses. Such roughnesses, if considerable, have an ill effect not only on the impression, but chiefly on the leather in the printing frame. If the scraper is of wood, the leather will suffer less, but there will be caused grooves in the scraper that must be planed out again, because otherwise each following impression will show a more or less plain streak. If the scraper is of metal, the leather may tear or the stone itself may be injured if the foreign substance in the paper is very hard. Therefore it is well to hold the paper to the light before dampening or printing and to remove any apparent defect of magnitude with a little knife.
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 circumstance 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 calledKühnel, and comes from a French factory. This paper has the property of depriving the stone of its preparation, and consequently to smut 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 smutting 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.
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 strongpressure 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 prone 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 scraper or the stone is not uniform and even, it is very prone 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.
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 illustration 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 moredifficult 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.
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:—
(1) It must not pull or shift 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.
(4) It must combine the greatest possible speed with this power.
(5) It must be easily operated, to save the workman.
All these qualities combined are not to be found in any press hitherto applied to lithography.
If we consider the peculiarities of book and copper print, we find a decided difference between them that affects printing importantly.
The letters of book-type are raised, the engraving in copper is depressed. It is evident that the former requires no such power for making impressions as the latter. Therefore the presses are so different that copper plates cannot be printed on a book-press and vice versa. Now, as the stone combines both the elevated and the depressed principles, the natural idea would be to combine the fundamental principles of both presses as nearly as possible for stone-printing. In book-print, only the types are exposed to the pressure, and in the average printed sheet these are only one fourth part of the entire surface. The remaining white space is not affected at all by the press. In the stone, however, the elevation of any part of a design is so slight that the entire surface is affected, and consequently a stone plate offers four times as much resistance. A book-press therefore would print a stone only if it were arranged for a pressure four times greater. Now, for a stone of the size of a letter-sheet the power required to print with one vertical pressure would be five or six hundred hundredweight, a pressure that could be supported only by a thick stone laid very exactly on a perfect foundation.
An ordinary copper-plate press increases the pulling of the paper somuch in the case of a stone plate that the impression would be worthless. This pulling is not caused, as in the case of the scraper, during the impression itself, as already described, but it is caused before the impression through the endeavor of the cylinder to force the plate along under it. Once the stone is under the cylinder, the paper is not pulled noticeably, because the cylinder glides over the leather much more gently and with much less friction than the scraper.
This defect might be corrected:—
(a) By supporting the cylinder so that it would come down on the stone only at the point where the print is to begin. But as the stone must be drawn pretty well forward for convenience in inking, this would demand that the cylinder be revolved forward and backward again as far as is needed for the impression, which means a great demand on the strength of the printers, not to count the loss of time.
(b) A second way would be to plane off a piece two inches wide from the cylinder at the point where the impression is to begin. The stone could be forced under this space readily, and when the cylinder revolves, it presses forcibly at once without pulling the paper very much.
(c) The press might be fitted with iron wheels with cog teeth to engage similar cogs on the cylinder. This would prevent pulling, but the mechanical work would need to be very accurate.
(d) The best arrangement will be the following: Set the upper cylinder so high that the stone can be brought under it without touching. Then bring it down with a screw, or better still, with a lever that can be operated by the foot.
The first figure in theplateshowing presses represents about how a copper-plate press is to be fitted for this work. On the whole, this is an ordinary copper-plate press, but the upper roller is set with its two axles or spindles in two iron levers, each of which is fastened to a piece of wood with iron screws one inch thick. Each of these pieces of wood is covered with strong sheet iron and can be adjusted higher or lower with two screws or with underlay of pasteboard. This is necessary that the press may be adjusted to varying pressures. The two other ends of thetwo levers, in which the cylinder sits, can be raised or lowered, so that the cylinder also can rise or sink. Now two springs or two weights are so adjusted that the cylinder with the levers always remains elevated. To force it down on the stone, an iron beam enters both sides of the press with two pegs so adjusted that when the beam is turned ninety degrees the levers are depressed at least two inches. As the cylinder is about in the middle of the two levers, it will thus be depressed one inch, which suffices to permit the stone to pass under it freely while it is elevated and gives the greatest pressure when it is depressed. However, the upper cylinder must not be one inch distant from the stone, but at the most only one fourth inch, for the remaining space of three fourths inch is required to provide margin for the elasticity of the various materials, and also to give margin for increased pressure whenever demanded.
On one end of the iron beam with the two pegs is an arm or lever which is joined to a thin stick with a treadle. This tread is so arranged that it remains elevated of itself. If the pressure is to reach sixty or more hundredweight, it must not be fastened directly to the treadle, but a second lever is required which is affixed to the side of the press.
Without going into tedious detail I cannot further describe this press. Mechanicians will understand me readily and perhaps be able to add many improvements. My belief is that a copper press so arranged would diminish all danger of squashing and pulling the impression, furnish powerful pressure, permit overlays of felt or fine cloth, and make possible considerable facility and celerity, which is a great advantage, because impressions always are better if too much time is not lost between inking and printing.
To safeguard the stone against cracking in such a press, the following points are to be noted:—
(1) The stone must be ground very true on the under side as well as the upper.
(2) Both cylinders must be perfectly true, and care is to be taken particularly that one cylinder is not thin toward the middle and the other thick, as this would easily crack the stone lengthwise.
The board on which the stone rests must be equally true and uniformly thick. At the same time it must be very thin, only one half inch thick at most. It will get very heavily squeezed during the printing, and the more the impression approaches the centre, the more concave will it become. The parts farthest from the point of pressure then resist unduly if the board is thick, and thus become the chief cause of cracking the stone. If the rollers are very true and the stone is very uniform, it is almost impossible to crack it if it is passed between the two rollers without a board underneath. If the board is thin, it is as if it were not there.
I believe that competent mechanicians can improve the present presses greatly.
Most owners of lithographic printeries have tried their hands at inventing presses, but in the end it has always been something based on the scraper or the cylinder principle. I myself have made more than twenty designs. Some were very useful and had advantages either in power or convenience, but generally were handicapped by some defect, so that I cannot even say with certainty which was the best of them all. So much depends on the mechanic's execution of one's plans, and a perfect design can be so spoiled by a workman that it is worthless.
I will, however, recount the best that has been done so far for lithography.
In Munich two kinds of stone presses are mostly used. They are:—
(1) The lever press, or, as the workmen generally call it because of its form, the Gallows Press.
(2) The Cylinder or so-called Star Press, the latter term being used because a star-shaped lever is commonly used instead of a crank to turn the rollers.
I have tried and found good the following:—
(3) A press with double levers.
(4) A gyrating or sliding press.
I know also—
(5) The roller press used by Herr Andre.
(6) And the press of Herr Steiner in Vienna.
Herr Müller in Karlsruhe and Herr Ackermann in London have a press with paper cylinders the construction of which is unknown to me.
This was the first press that I used with advantage, and it is used still in Munich in all important establishments for work that demands speed particularly. It would be an excellent printing-machine in all respects if it did not have the defect that its power cannot be increased much more than six hundredweight without forcing the workmen to undue exertions. Therefore it is no longer available for large plates or for works that require immense power. It is very good for pen designs not larger than a letter-sheet, and two workmen, one to ink-in and the other to print, can produce twelve hundred impressions in a day without hardship.
The pressure is produced by a lever six to twelve feet long, fastened to the scraper below and to a spring (an elastic board) above. It is connected with a tread, and when forced down, presses with the desired force on the scraper and so on the plate. The board holding the lever overhead must be partially movable like a spring because the lever describes a part of a circle on the plate below. Hence the pressure at the beginning and end of the impression is not so great as in the middle, and great care in choice of wood and manufacture is demanded to give the spring board the necessary elasticity and power combined. I have found a board of young dried pine the best, the dimensions being six feet long, eight inches wide, and two inches thick, provided that the fibres all ran lengthwise. It is not always possible to find a good board at once. Often I have found that the difference between two boards made a great difference in the effectiveness of two presses otherwise exactly the same.
The scraper arm consists of two parts, of which the shorter one, to whichthe scraper is fastened with a screw, is only one and one quarter feet long. The other part is as long as the height of the press permits. The higher a lever press is, the better is it, because then the circular motion described by the scraper wood approaches a straight line more and more, so that the press exercises a more uniform pressure during all stages of the impression and is easier to handle. The second illustration shows this kind of press in the moment when the impression has been finished, the printing-frame opened, and the scraper arm swung back again.
The printing-frame is much like a book-printing frame, and is furnished inside with a second small frame which holds the paper, being furnished with small springs or strings. When the frame has been turned over the stone, the paper must be at least half an inch from the stone to avoid smutting, which will occur if it touches. The paper must not touch the stone till pressure is applied, and then only on the spot pressed downward by the scraper.
As soon as both parts of the scraper arm are in a straight line, so that they form practically one piece, the scraper wood is pulled down and the printer draws it toward himself over the printing-frame and the stone plate. At this time the following is to be observed:—
(1) Both parts of the arm must be so fastened to each other that they may be bent like a knee, but once they are straight in line, they must stay in that position. It is well, therefore, so to adjust the parts that they will not be directly over each other, but rather exceed a straight line under pressure, and bend a little inward. The position of the scraper must be considered also. On the whole the following rule holds good: the point where both parts are united with a nail or a screw must not be in a perfectly straight line between the point where the scraper rests and the point where the arm is fastened above, but should be at least two and a half inches forward of that point. Otherwise the arm may spring outwards toward the workman and injure him severely. The third illustration shows the construction of the scraper arm and the scraper.
(2) The arm must be grasped as low as possible when being drawn toward one's self, in order to diminish the danger of springing outward.
(3) The workman must press his body tightly to the table of the press to get proper leverage. Standing free, a man of moderate strength could not move the scraper at all when the pressure is on, but a man standing in correct position can do it without difficulty.
(4) Under very heavy pressure the inker-in, who stands on the other side of the press, can help by pushing.
The scraper is a piece of pear wood as long as the size of the plate demands. Its height is about four inches, its thickness one inch. The end that rests on the leather is trimmed down so that it has a thickness of only one line. This end must be especially true and planed to fit the stone, also neatly rounded off. It should be so fastened to the arm that it may be adjusted to the position of the stone. The stone does not always lie truly horizontal in the press, sometimes because it is not uniformly thick, sometimes because the underlay is not quite even, and sometimes because the press itself has been a little strained. If the scraper has been made properly, it will adjust itself to the stone, even if the scraper arm is not quite plumb on the stone, a condition that often occurs with small work, such as titles and other things that are at the end of a stone.
(5) For every press a number of scrapers of different dimensions must be in stock. Generally a lever press is so made that the printing-frame can be raised or lowered according to the thickness of the stone. Then the scraper must be changed accordingly.
(6) The connection of the upper board with the tread is made by a thin stick that is fastened to a lever below, by means of a small iron piece which contains several holes that serve to adjust the height of the tread according to need.
(7) The leather in the printing-frame is strong calfskin. It must be stretched very evenly and tensely and must be smeared from time to time very thoroughly with tallow.
(8) On the outer side of the frame there are four wooden strips that can be adjusted as desired. One serves to show the point where the impression is to begin. Another shows where it is to end. Both must be so strong that they can resist the scraper. The other two are adjusted at the sides and guide the scraper.
When Herr Professor Mitterer installed a lithographic institution for the Feyertags-Schule, the lever press appeared to him to demand too much labor, especially when powerful pressures were desired. He invented the so-called Cylinder or Star Press, which has its place in most establishments, especially those in other countries. It has had minor changes made in it by many persons, but on the whole, nobody has succeeded in improving it notably, except for a considerable improvement made by Herr Mitterer himself. My description will include this improvement.
The cylinder press might almost be called a reversed lever press. Herr Mitterer borrowed from it the idea of effecting the impression with a scraper, but he did not let it move over the plate, as in the lever press. He gave the scraper a fixed, immovable position while the stone was drawn through underneath, thus making his press resemble a copper-plate printing-press somewhat.
Illustration number 4 shows this machine in the moment when the impression has been made. In the middle of the machine is a cylinder ten to twelve inches thick and as long as the breadth of the press. It has strong iron spindles that revolve in well-lubricated brass bearings. Above the cylinder is a board on which is fastened the stone with the printing-frame. The scraper is on a strong lever that is held up by a counterpoise. When everything is ready for printing, the scraper is forced down. By means of a strong iron hook it engages the treadle and thus can be pulled down with the utmost tension. Then the cylinder is turned by means of two levers affixed to the crank, and this draws the stone and printing-frame through under the scraper. One workman alone can do this under ordinary pressure, but an appliance at the other end of the press enables a second workman to help.
I have already mentioned the gyrating scraper press. I have improved it considerably. It has the form of the ordinary lever press, but all the parts can be much lighter. For instance, the lever is only one and a half inches thick. The spring (the elastic board) is very elastic and need exert a pressure of only one hundred pounds. The little scraper is only an inch long and presses on the plate with a force of fifty pounds. The press is useful for very thin stones that might crack under greater pressure. The pressure, nevertheless, is great, because it is all exerted on such a small area. The press has two defects. It is easy to miss many parts of the design with the small scraper, and the paper is likely to stick to the leather, producing poor register. I have obviated these faults with the following invention: A large scraper is fastened to the lever to press on the plate with a force of one hundred pounds. A small one is fastened to this in such a manner that it can be moved to and fro easily. While one workman rubs to and fro with the small scraper, another draws the entire stone and printing-frame slowly along under the large one. If good underlays are used in addition, this process will produce beautiful work that cannot be produced so well with any other machine. However, a large field is left in this form for improvement.
The fact that the concentric motion produced by a single lever can be transformed into an almost straight motion by use of a second lever, led me to design a double lever press, which has turned out very successful, giving great force with speed. As its description would demand much space, and since on the whole it ranks equally with the improved cylinder press, I offer to send models to those who desire to have everything useful for the art.
The cylinder press of the Chemical Printery in Vienna would, without question, be of excellent service for the art if it were more powerful. Its construction is as follows: The stone is fastened to a table with the printing-frame which has fine felt instead of leather. To make the impression a brass cylinder eight inches thick is rolled over it. As this cylinder would not produce enough pressure from itself, despite its massive make, two iron beams are fastened to the axles. They pass through the table and are fastened to a box that contains iron or leaden weights. Unfortunately the space prevents the use of more than five or six hundredweights, and this is too little for the large surface of the cylinder, thus forbidding any sharp, clear impressions.
This kind of press could be greatly improved if it were built higher to give more room below for weights, or the beams could be lengthened and passed through the floor into a lower room, thus giving space enough to add weights up to fifty and more hundredweight.
The press of Herr Andre is much like this, except that its cylinder is only three inches in diameter and that it is forced on the stone not with weights, but with a lower cylinder that presses upwards. It prints fast, like the other, but does not possess enough power.
In conclusion, I must remark that the concentration of ideas caused by writing this chapter has led me to begin experiments toward making a lithographic press which shall leave nothing to be desired. As soon as my affairs permit, I shall execute this on a large scale, and if the result fulfills my hopes, it will be a pleasure to describe it accurately to all friends of my art, or to furnish them models at cost.
There are two principal methods of stone-printing, Relief and Intaglio.
In the former, the fatty parts of the stone are not attacked by the etching fluid, while the rest of the stone is dissolved more or less. Therefore the fatty places are left in relief.
In the second method, the design is either engraved into the stone with a sharp steel instrument or etched-in with acid.
The relief method has the advantage of greater speed and, generally, a greater number of impressions. It is easy for the artist to apply, especially in crayon work. The intaglio, however, makes possible finer and more powerful work, and again, in many cases, is the easier of the two for the artist. Therefore it is impossible to say in a general way which is the better. It depends on the work to be done.
To this method belong principally: (a) Brush and pen designs; (b) the crayon method; (c) the transfer method; (d) the wood-cut method; (e) a sort of scraped style; and (f) spatter-work.
This is one of the best in lithography, and perhaps the best, because it touches daily needs most directly. It can be used not only for allkinds of writings, but also for illustration that does not demand the supreme perfection of copper plate. The ease of manipulation, the speed and the almost countless number of impressions recommend it especially. It may even be prophesied that in future, when true artists have become better acquainted with it, it will be used for high forms of art.
Much as this method has to recommend it, it has been used mainly for script and music, and it is difficult to gain adherents and followers for it. The reason is an apparently trivial thing, but it has made most artists averse to it. Since stone-printing exists I have found only two persons who could do anything with the steel pen at the first attempt. These were my brother Klemens, and a Herr Porner, who works now in the establishment of Herr Müller in Karlsruhe. All others have had to struggle more or less with this slight trouble, and yet it does not demand more than a few days of patience and study.
For pen work one must not be too particular in selecting stones, as the less perfect ones are more available for this than for any other method. However, the general rule holds good here, too, that the purest and hardest stones are best.
If they have been used previously, so that the fatty inks have penetrated pretty well, they still need not be ground too deeply, but it will suffice to grind them merely till all depressions and elevations of the previous design have vanished. They may be ground with sand or pumice, so long as they are made smooth so that no roughness can be perceived. The smoother and finer the surface is, the easier will it be to work on it with the pen.
To design well on stone with chemical ink, the stone must be prepared after grinding so that the ink shall not flow and spread. Dissolve one part of tallow in three parts of oil of turpentine and coat the dry stone very quickly. With a clean rag or tissue paper wipe it at once so thoroughly that the coating vanishes again almost entirely, leaving only a thin film that can be easily devoured and removed when the etching fluid is applied later. It is well to do this some hours before beginning workon the stone, partly to give the turpentine odor time to evaporate and partly because it is easier to work after a little while than immediately after coating the stone. The stone can be prepared far in advance, even so long as some months before using. In that case it is necessary merely to clean the dust away with a cloth or fine brush. This should be done anyway at intervals during the work, or it will clog the pen.
I prefer another way of preparing the stone for designing, because it is one that insures the stone against containing any hidden preparation, which can easily occur in grinding owing to carelessness or uncleanliness on the part of the workman, especially if many old plates are being reground, when the gum which most of them contain from previous use will mix with water during grinding and thus form a partial preparation of the stone.
I coat the plate with strong soap-water containing many soapy particles, and dry it off as well as possible. Now, there will be too much alkali on the plate, which will not be good for fine work. I pour a few drops of clean water on the stone, make it quite wet with this and dry it again thoroughly. The fat of the soap will then have precipitated itself on the stone and at the same time has lost all alkali. The soap-water must not be too thin, as in that case it will precipitate too much fat on the plate at once and the etching fluid will not be able later to destroy it properly. This would mean the total destruction of the design. To make quite sure, I advise beginners, after applying soap-water and drying it, to coat the stone with the tallow and turpentine solution, clean it quickly, and thus be absolutely assured that the plate is thoroughly prepared for the design.
It must not be imagined that this preparation for work is not very important. I am convinced that less depends on the quality of the ink than on a surface freed from all acid and mucous substances and provided with a sufficient amount of fat.
On the stone thus prepared the rough design may be done with lead crayon or red chalk or by tracings or transfers. Any surplus of lead or red chalk would make trouble during the succeeding completion of the design with chemical ink, and must be removed carefully. If the designhas been laid on by transfer, the resultant fattiness must be lightly rubbed away with a fine sand, but not so as to injure the design.
This method, of first drafting the design on paper with soft chemical transfer ink and then transferring to stone, offers such advantages that it pays to practice it. Care must be taken to remove all surplus of color, as otherwise all lines that should not appear will resist the etching fluid and gradually show again. Those who fear destruction of the design by the use of sand can effect the same purpose by printing off on clean waste paper a few times, or the design may be printed off on paper before being transferred, thus cleansing it of surplus fat.
When the design has been laid on the stone clean and strongly with chemical ink, the plate can be etched and prepared, but not till the whole design is perfectly dry, because otherwise it cannot resist the action of the fluid.
The parts finished first usually are dry long before the entire work is finished. A trained eye can recognize the proper degree of dryness from the sheen, which varies with different kinds of ink, but on the whole is always duller when the design is dry than while it still is wet. It is highly necessary that the design be thoroughly dry. It is possible to keep a designed plate for years without etching it, so long as it is protected against injury.
Etching is done in two ways, painting the fluid on and pouring it on.
The former method is less circumstantial, but is used only in coarser work, because there is always danger of damaging delicate parts of the design. It has the advantage, however, that any dirt caused by corrections will be removed. A mixture of three or four parts of water with one part of aquafortis is painted over the stone with a soft brush of fox- or badger-hair. The brush must be dipped continually because the fluid loses its power.
For the second method the stone is placed in a large wooden trough or box, provided with cross-pieces to keep the stone from the bottom. The acid, thinned down with thirty or forty parts of water, is poured over it. It is rather immaterial how much one may dilute the acid. Very weaksolutions simply mean that the pouring must be repeated oftener. The fluid acts on stones according to their degree of hardness. Regard must be had, too, to the delicacy of the design, very fine lines being unable to resist etching that does not affect coarse lines.
Only slight experience is needed to recognize the effect of the acid. By looking at the stone sidewise and against the light, the growing elevation of the design can be perceived easily. When the fatty coating caused by the soap or turpentine wash has been etched away completely, and the water adheres equally everywhere, the stone generally is sufficiently etched to be ready for preparation and printing.
For the sake of easier printing, and also so that future grinding and any desired improvement may be done on the stone, there should be a little more etching, if the design is not too delicate. But if the design is very fine, the etching absolutely must not be more than strictly necessary, because the fine lines might easily be eaten away. Coarser designs can bear strong etching which often may reach the depth of a thick paper. But an inordinate amount of etching is not to be recommended, even if the design can bear it, because the edges of a deeply etched line are rough and take the color so strongly that it works into the cavities and is very hard to get out.
When the stone has been properly etched, clean water is poured over it to wash away the free acid. Then the work of preparing the plate with a solution of gum arabic in four or five parts of water can begin at once, or the stone may be set aside to dry, thus giving the finer parts of the design, that may have been most affected by the acid, time to adhere again to the stone and soak in, which can occur only in the dry state. This is entirely unnecessary with most pen drawings, but with brush and especially with crayon work it is of great value.
When the stone has been prepared with gum, it is set aside to rest for a few minutes. Then pour a few drops of water and exactly the same quantity of oil of turpentine on it, spread it in all directions uniformly and wipe the entire design off clean with a woolen rag. Hard ink, especially if it has been on the stone for some time, is more difficult to remove and a little more turpentine is required.
The stone should now be inked-in at once, because the turpentine, and with it all the fattiness, is liable to extensive evaporation, and then the stone will not take color well.
Inking-in of the pen designs is done as follows: A clean linen or woolen rag is soaked in clean water and wrung out till it is damp rather than wet. This is passed over the whole stone so that it becomes a little wet everywhere. Immediately after this dampening, the well-inked printing-roller is passed to and fro over the plate several times. The roller must be lifted frequently during this work so that the points of contact change. To lay the color on well and quickly, the roller should be held rather firmly in the beginning, well pressed down and used with a certain rubbing motion that will tend to lay color on the design sideways, so to speak. Then the roller must be allowed to roll to and fro a few times without much pressure, to spread the color and take away any surplus. Do not roll too long, till the stone dries, because then it will take dirt immediately. Should this occur, it must be wiped instantly with the damp cloth till it is clean again. If dirt is left too long, it will be extremely hard to remove.
Beginners usually wet their plates excessively to counteract this trouble of drying during the inking-in. This results in wiping away fine strokes, and the roller gets so wet that no good impression can be made till it has been dried sufficiently again. For this reason beginners should not use bath-sponge, because, though it is excellent, it leaves too much water on the stone unless one knows exactly how to use it.
Some printers put a little gum, others a little aquafortis into the water to wet the stone. Others use stale beer, or even urine. I consider all this unnecessary, if the stone has been prepared correctly and the color is good.
I have described the ink-rollers. I repeat that they must be uniform, soft, and elastic.
As to the inking-in color, I am not able yet to lay down a strict rule. All that I can say, as a result of my experiments and experiences, is:—
(1) The firmer the varnish in a color is, the cleaner is the work of inking-in.
(2) The same is true the more lampblack it contains.
But in both cases the finer parts of the work are easily rubbed away, and too much lampblack makes the lines squash the impression.
(3) The toughness or fluidity of the color must bear correct proportion to the power of the press. The harder the varnish, the more power is required in the press.
(4) Tough varnish is not so liable to squash under pressure, but if it has once been pressed into the spaces between the lines of the design it is not readily removed by the mere action of the inking-roller, and this causes more and more smutting and, finally, total ruin to the stone. Generally when a tough color has adhered too much, there is no other remedy than to clean the stone well with gum and oil of turpentine; and this, if done too often, damages the preparation and makes the impressions continuously poorer.
(5) Soft color spreads more readily under pressure, but is removable after each impression by merely dampening the plate.
(6) In using soft color, the paper may be kept damper than with hard colors.
(7) Soft as well as hard printing-color, if not mixed with the proper amount of varnish, has the property of producing poor, sooty impressions because of a defect called shading. Shading is caused as follows: If a drop of oil falls into a basin of clean water, a part of the oil will spread immediately. Now, a stone is wetted before inking-in. After the inking a considerable portion of dampness remains. If the ink is very fluid, it will happen often that a part of it will spread away from the design to the surrounding moisture, producing something that looks like a shadow around every part of the design. This does not occur instantly, as in the case of the pure oil, but gradually, so that it is not as noticeable when the swifter lever press is used as with the slower cylinder press or if the workmen are slow. If a stone can be dampened so exactly that with the last touch of the ink-roller the last vestige of dampness is removed, thisis not likely to happen. But it is difficult to arrive at such accuracy. It is better to add enough lampblack gradually to the varnish to make it lose its elasticity, when the shading effect will cease.
(8) While shading is obviated largely through enough intermixture of lampblack or other coloring substances to take away the fluidity of the printing-color, this intermixture will cause other troubles. The finer places will not take the harder color so well, whereas at other places too much will be taken. Also an impression made with much lampblack will off-set more than one made with color in which varnish predominates. Neither will the impressions be so black. Experience teaches that a printing-color that has less lampblack will be blacker, because the sheen of the varnish will make the color strong and lacquer-like. I have tried to invent a kind of varnish that would not be so liable to shading and thus would permit a greater fluidity with safety, but lack of time has prevented me from exhausting the possibilities. I am sure, however, that it can be done, for I have found that the common linseed oil varnish can be made to lose its property of shading by admixture of fatty and resinous bodies. For instance, the addition of a slight amount of Venetian turpentine permits a greater fluidity. Very good is the following composition: Six parts linseed oil, two parts tallow, one part wax, melted together and thickened by boiling down and burning like the ordinary linseed oil varnish.
(9) The inner composition of the stone and the temperature have a considerable effect on the print and also react on the color. A stone, especially a porous one, has much less internal moisture on very warm, dry days. Then the dampening done before each impression often evaporates instantly and unequally, so that it is difficult to ink-in uniformly with a soft color or one lacking varnish, unless one wets the stone unduly, which, again, injures the impressions. In that case one must use a color that is firmer than should be used according to ordinary rule. It is also well, before printing from the stone, to lay it in clean water for a few hours, or overnight, so that it may soak in enough moisture to make it easier to dampen.
(10) If the drying of the printing-color is to be hastened, as is necessarywith some work, a little finely powdered mennig may be mixed in. Finely powdered litharge of silver dries still better, but only a small amount of printing-color must be mixed with it, because it toughens within an hour. It will not keep for another day, because the mennig will dissolve after a while.
In printing from the pen design, the following must be observed:—
Even if the stone has been inked-in uniformly and well with a good color, the impression can be spoiled in various ways: if the paper has not been dampened as required by the nature of the color and the power of the press; if the pressure is not in proportion to the consistency of the color; if the scraper is not even, and if the leather is not properly stretched.
Therefore care must be taken in printing pen designs:—
(1) The paper must not touch the inked design till the scraper forces it down. It is not advisable to lay the paper directly on the stone. It should be in the printing-frame, which, as already described, should be so arranged that it will keep the paper at least one fourth inch away from the stone.
(2) The proper dampening of the paper is not a matter of the greatest importance in pen designs, so long as it is not too wet, in which case it causes squashed impressions, does not take color uniformly, and, if the printing-color is tough, will stick to the stone. In general, the rule holds good that the degree of dampening must be in proportion to the firmness of the varnish, and that a softer varnish permits increased dampening. Dampening is done chiefly to soften the paper, and the qualities of the paper dictate the amount necessary to a large extent.
(3) The tension of the press must be more powerful with hard printing-color and carefully graduated with soft color. Besides this, it depends—
(4) On the structure of the scraper. If it is not absolutely uniform and well fitted to the stone, more power is needed. Thus the defect often is corrected; but this may make the color squash and spread in other spots, therefore it always is better to correct any defects in the scraper. The sharper the scraper is, the clearer are the impressions, because then the whole force of the pressure concentrates on the smallest area. But usuallythe scraper soon becomes dull, and then the press must have more power.
(5) Insufficient tension of the leather also may produce poor impressions, especially if the color is soft and the paper very wet. Therefore as soon as impressions appear blurred and squashed, the leather should be tautened and well lubricated with tallow.
Now we come to an important matter, namely, the correction of errors. It does not happen often that a drawing or inscription can be made entirely without error, and it would be a great imperfection in lithography if these mistakes could not be corrected at once.
Errors may be observed before etching or afterward. Different ways of making corrections are required.
It is very easy to make corrections before etching. If the error is observed as soon as it is made, while the ink still is wet, it may be corrected by merely wiping out the defect with the finger. If the ink is dry, oil of turpentine is required. In each case the ink must be well removed so that it will not resist the etching fluid later. If only tiny spots are defective they can be corrected by delicate use of a sharp eraser. Defects that need merely to be destroyed without drawing anything else in their place may be scraped off with a knife or with pumice stone.
After the plate is etched, errors demand treatments that differ according to whether a defect or blemish is merely to be removed, whether something else is to be drawn in place of the removed part, or if something has been forgotten and is to be added. The area of the correction also makes a difference.
If it is only a matter of removing small defects or places, delicate erasure will do. The same, or polishing with pumice, is done if the area is larger. Then the corrected spots must be coated with a mixture of gum and aquafortis, using a soft brush very carefully that it may not touch any of the sound places.
If something new is to be drawn in, the process is different. Ink-in the stone very clean, and coat it with gum and water that is very thin and delicate. Let it dry. Then scrape the defective places away very carefullyor grind them away by rubbing with pumice stone. Coat the spots cautiously with soap-water or oil of turpentine and clean off again as thoroughly as possible. (This coating is not necessary in the case of a few isolated small lines or points.) Now draw in your new design with chemical ink, and as soon as this is dry, etch the corrections carefully with a small brush and then prepare with gum.
The third case, where something has been forgotten, is treated almost the same way. If it is only a very small thing, the stone need merely be scraped carefully. Then the drawing may be put in, preferably with a thicker ink. If the area is large, the stone must be ground where the design is to be added, coated with soap-water or oil of turpentine, and then treated as explained before.
When the stone has been corrected and prepared for printing, it can be used at once or set aside for some length of time. In the latter case it should be inked with a firm color and coated delicately with gum solution. Then it can be held as long as desired. Coating with gum solution is advisable not merely for storing away, but for every interruption of printing that lasts more than five minutes.
If a stone has stood longer than a day without being freshly inked, it must be wiped off first of all with gum solution and oil of turpentine, that it may take the color well, so that the very first impression may be perfect. During the progress of printing, the following points are important: Uniform distribution of water, the same of printing-color, frequent inking of the inking-roller, and the very greatest speed possible.
In the main points the brush process is like that of the pen. The chief difference is that it is not possible to make the brush strokes as strong as those with the pen. Therefore, brush work does not resist etching so well and must not be treated too powerfully. Much depends on the treatment of the brush and the consistency of the ink. The brush does not permit such a flow of ink as does the pen, and generally requires one that is more fluid. A good brush ink is made as follows:—
Mix two parts of pure white wax and one part of good tallow soap into a mass not larger than a hazel nut. The ink loses its good propertiesquickly and should be made fresh day by day. Mix the two materials with a thick knife on a lukewarm (but positively not warm) stone, separate into small parts and moisten with rain water. As soon as the water has softened the mass a trifle, add as much lampblack as will lie on two knife points and mix the whole mass together once more till it is thoroughly mixed and quite firm. When required, a bit of this is rubbed down in a clean saucer with rain water.
As a better flow of ink is needed for brush work than for pen work, it is evident that it would not be requisite to treat the stone with soap-water and oil of turpentine, as for pen work. However, it often pays to make certain fine lines with the pen, and therefore it is better to combine both processes and prepare the stone as for pen work. It is well, however, after drying the coating, to rub it very gently with dry sand, which will not make the pen strokes flow to any extent and still will prepare the stone so that it will take the brush strokes well and not make necessary such strong etching.
If a brush design is to be etched in high relief, for ease in printing or for durability, it must be etched only to the extent absolutely required at first. Then it must be prepared with gum and inked-in with good acid-proof color. Set it aside for a while, that the color may concentrate so that it will resist the acid well, and then etch the stone to the desired degree. After etching, wash with water, coat with gum and put aside to dry. Owing to this latter procedure any fine parts that may have been unduly affected by the acid will adhere to the plate anew and it can be printed then like a pen design.
If pen and brush work are to be combined on a stone, and absolute certainty is desired, that even the very finest lines shall not suffer from etching, the following process will serve:—
Over the cleanly ground plate pour a solution of weakened but pure aquafortis, about forty parts of water to one part of aquafortis. Repeat this several times. Then pour a great deal of water over the stone, to wash off all acid, and let it dry. Pen as well as brush work is easy on such a stone, by using the proper ink for each method. When the work isfinished and dry, the stone is merely coated with gum solution. After a few minutes it can be inked-in with acid-proof ink and treated as described before.