APPENDIX.
1. NEGATIVE TRANSFER WITH BICHROMATED GELATINE PAPER.
THE properties of bichromated gelatine paper can also be very well used for the so-called negative printing, and this method offers many advantages.
In order to convert a positive printing image into a negative various methods may be used; the most convenient for the lithographer is the following:—A good litho stone is first ground in the ordinary way and then the surface rubbed with a pad and oxalic acid solution till it has a high glaze or polish. On to this stone is then transferred a sharp impression in a non-greasy ink from the positive printing image. According to the destination of the stone for large or small editions one of two processes may be adopted. If a thousand or more pulls are required from the stone the transfer may be dusted with resin powder, and this melted with the burning, heating, or ether process and the drawing etched in relief with 8 to 12° nitric acid and gum. Then the stone may be well washed with water and the acid removed with one to two per cent. acetic acid.
For small runs the first etching is omitted, and the stone treated with acetic acid. In both cases the stone should be well washed, dried, and then coated with dissolved lithographic tusch or autographic ink. The greasy substances of these materials penetrate into the surfaces of the stone that are laid bare, and firmly adhere. When the tusch or ink is completely dry the stone is washed with turpentine, inked up, and one now has a negative image from the subject in question, which shows all the original printing places in white and all white places black.
The process of preparing such negative prints by the use of bichromated gelatine papers is much simpler.
A sheet of gelatinized paper is sensitized for this purpose on a 5 per cent. bath of potassium bichromate, squeegeed to a sheet of plate-glass and well dried, and on this is made with black ink, which is very opaque, in the dark or in gaslight, a sharp clean print. This print is then laid on a flat cable, under a sheet of plate-glass, so that it cannot roll up, and exposed to the light for from five to thirty minutes. A long exposure rarely does harm in such cases, as the good opaque black ink allows no rays of light to pass through to those places which later should print white.
The next manipulation is the development and inking up, which is done as in ordinary photo-lithography. In this operation all {84} those places which were not covered up by the printing will take the developing ink; on the other hand, those places where the impression was will wash out clean and white. The print has assumed the appearance of a photographic positive. The print is now treated like any other photo-lithographic print, and finally transferred to a stone or zinc plate. This method is distinguished by its simplicity and safety; it has also the advantage that any desired printing subject can be directly transferred in negative form to a zinc plate for relief etching, which otherwise could only be done by preliminary transfer to stone and subsequent transfer to zinc.
2. PHOTO-AUTOGRAPHY. DRAWING WITH AUTOGRAPHIC INK OR LITHOGRAPHIC CHALK ON A CYANOTYPE, SALTED OR OTHER PRINT FROM A PHOTOGRAPHIC NEGATIVE OR POSITIVE.
By autography we understand that method of reproduction by which any writing or drawing is made on a prepared or not prepared paper with greasy ink, tusch or chalk, which is subsequently transferred to stone or zinc for printing, or to zinc plates for relief etching.
Autographic drawing papers differ for the different purposes, and for writing and simple line drawings smooth hard post paper is used, and lined transfer paper for fine pen or chalk drawings. The latter are prepared commercially by Angerer and Göschl. Very beautiful grained drawings can also be made for transfer on pyramidal grain paper. The proof for such drawings is usually done with lead pencil or red chalk, or it may also be made on a gelatine proof.
In order to obtain fully and completely the character and correct reproduction of the drawing, without special expense of artistic help, it is advisable to use a photographic print as proof. It should be noted that for pen drawing on smooth paper with greasy tusch or ink, for chalk drawings on a prepared grained paper done as previously mentioned, with greasy lithographic chalk, the drawing should be transferred direct to zinc or stone in order to save having to make subsequently a photographic print.
If a pencil, red crayon, or other proof is used for an autographic drawing on paper with the idea of transferring it direct to stone or zinc, a suitable photographic print may also be used on suitable paper without any disadvantages.
For the prints all photographic papers without glaze, such as ordinary plain salted paper, Eastman’s positive bromide paper, and others, may generally be used. Glossy or albumenized papers are not suitable for this, as the ink runs, and does not form solid clean lines. {85}
The best of all, however, is cyanotype paper, as even with very deep printing it keeps the details in the shadows open, and on account of its blue tones is more suitable for the subsequent drawing with black tusch. When, however, prussiate paper is not handy, and subjects with fewer shadows and less details are to be treated, any of the other papers above-mentioned may be used.
If ferro-prussiate paper is to be used, the same may be prepared as recommended on p. [23.]
The so-called salted or plain paper is prepared as follows:—A sheet of well-sized post paper is first bathed in a solution of—
| Ordinary salt | 1 | part |
| Water | 25 | parts |
and then sensitized in a solution of silver nitrate 1 : 12. It is printed till the print has assumed a fairly full brown tone, and all the details in the shadows are well printed out. It should then be toned in the following toning bath:—
| Distilled water | 1000 | g. |
| Sodium acetate (twice fused) | 15 | g. |
| Solution of gold chloride (1 : 100) | 25 | g. |
till the print has assumed a deep dark brown tone. It should then be fixed in a solution of sodium hyposulphite, 1 : 15. It should be printed rather deep, as in toning and fixing the image loses in depth. It is moreover unnecessary in this case to make a beautiful print; the chief thing is only that all details of the image should be clearly seen. The print is then well washed in frequent changes of water and then dried.
The print on Eastman’s bromide paper is prepared as follows:—
Red light must be used. It should be printed by an ordinary gas flame at a distance of about 50–80 cm. (= 24 to 36 ins.) for 1 to 20 seconds, according to the density of the negative. Here again a technically perfect print need not be arrived at, but one which contains all the details very clear. Under a good transparent negative a useful image for the artist will be obtained with about two seconds’ exposure.
The developer is composed of two solutions:—
| (A.) Water | 500 | g. |
| Neutral oxalate of potash | 165 | g. |
| (B.) Water | 50 | cm. |
| Sulphate of iron | 15 | cm. |
| Concentrated sulphuric acid | 2 | drops |
| Or glacial acetic acid | 5 | drops |
Three parts of solution A and one part of solution B should be {86} mixed together. As soon as the shadows have attained the desired tone, the prints should be placed in several fresh baths of
| Water | 200 | ccm. |
| Acetic acid | 1 | drachm. |
| Sat. sol. alum | 50 | g. |
and then washed and fixed in a bath of
| Water | 50 | ccm. |
| Sodium hyposulphite | 10 | g. |
for about ten minutes. Then well washed and dried.
For pen drawings all not gelatinized or albumenized printing papers may be used as already mentioned. The chief thing is that the paper should be well-sized and of good firm texture. If prepared grain paper is used, which is provided with a film of chalk, kaolin, or any other white colouring matter combined with gelatine, and on which film the grain is impressed, only prussiate prints can be used. The paper is sensitized as previously described, only it is advisable not to leave it too long in the solutions, or else the film may become softened. The film will also dissolve in hot water at about 80° C.
The prints as soon as dry can be used for drawing on. On the grain papers the outline may be drawn with the pen and be shaded with chalk, or it may be drawn with chalk only. With unprepared papers it is advisable to coat them with a thin solution of boiled starch, as then the transfer to zinc or stone is most exact. The drawing may also be left a long time without spoiling. The coating is performed with a pad dipped into the liquid, which consists of one part of fine bookbinder’s starch and four or five parts of water, and passed several times over the print.
The drawings ought only to be done with greasy lithographic tusch or chalk or autographic ink, which consists principally of greasy materials and lampblack. For pen drawings hard pens should be used, and care must be taken to make thick strokes. Only a little tusch or ink ought to be taken into the pen, so that it does not run out, and thus clean, sharp lines be obtained. If this be observed very close shadings and cross lines can be produced clean and neat.
When the drawing is finished and the tusch or ink has become dry the same should be laid between damp blotting-paper, and meanwhile a clean ground, and dry pumiced stone worked in the press and the pressure correctly adjusted. As soon as the drawing has become moderately damp right through, and the paper feels soft without being wet, it should be laid with the image downwards on the stone and transferred to the same with strong pressure. After repeated working the paper will adhere firmly to the stone. In order to loosen it the stone should be covered with hot water of about 80° C., when the film will dissolve and the paper become quite free. Any exertion of force must in this {87} operation be quite avoided, and the paper must not be pulled off with violence. All, even the finest lines, will have been transferred to the stone. The stone is now gummed, if possible allowed to stand for some hours, and then etched with a gum etching solution of two degrees’ acid strength, or later etched in relief, and is ready for printing. If the transfer is made to zinc, for printing from this the plate is treated as suggested on p. [6.] If, however, a relief etching for the typographic press is to be prepared of the subject, the transfer is made on to a smooth polished zinc plate.
3. LITHOGRAVURE.
With this particular process an intaglio printing stone or intaglio printing plate is prepared by chemico-physical means.
This process was discovered and brought to great perfection by Chas. Eckstein, the general director of the Typographical Bureau at the Hague, and offers especially many advantages for the reproduction of maps.
A map engraved, drawn, or transferred on stone, or written in on copper, in originally one colour, can by this process in a comparatively easy way be converted into a many-coloured print; this process can also be used very advantageously for changing the names for the places—rivers, mountains, etc. In the first place intaglio original printing plates in all the colours can be prepared which can then be printed for further reproduction; in the second case it is necessary to re-engrave the network, hydrography, etc.
When it is desired to convert a monochrome image into a multi-coloured map, as many stones as there are colours to be used must be first ground and polished with oxalic acid till they have a high polish.
In the meantime an asphalt or other light-sensitive solution should be prepared, with which the stone is coated in the dark very evenly, and somewhat more than is done for a photo-lithographic print.
The asphalt solution is composed of—
| Syrian asphalt | 20 | g. |
| Chloroform | 300 | g. |
| Benzole | 100 | g. |
| Oil of lavender | 20 | drops. |
After it has been dried in the dark the impression from the black plate, which should be previously made on transfer paper, is transferred to the asphalt film as previously laid down, and before it is dry dusted with bronze powder. All lines, titles, or figures which should not appear on that particular colour-plate must be then covered with the above asphalt solution, and only those places, for example, on the one plate all titles, on another all the roads, on a third the river courses, and so on, should be left, all of which later should appear in printing. {88}
The stone is now, according to the sensitiveness of the film and the strength of the light, exposed for from fifteen minutes to two hours. Over-printing, if it is not very exorbitant, does not do any harm with the stronger letters or lines on account of the good covering. With very fine lines, however, more care must be taken. If there is any doubt as to the length of the exposure a test may be made at one corner of the plate with a pad dipped in rectified turpentine. When the asphalt will no longer dissolve the exposure may be discontinued. With some experience the photometer may also be used.
Then the whole surface should be washed with rectified turpentine and a pad of cotton wool, when the ink lying under the bronze, that is, the lines where the asphalt has been protected from the action of light dissolve, and the surface of the stone appears. The rest of the asphalt film has become insoluble from the action of light, and now forms the etching-ground for the reversed negative image on the surface of the stone.
When the stone has been well washed with water it may be etched, which is done with glacial acetic acid two parts, water 100. When there are any fine lines in the drawing the etching is interrupted at the end of two minutes, and they should then be covered with tusch, and then when the tusch is dry the other parts are further etched for a longer or shorter time according to the degree of fineness. In any case the time of etching should not exceed five minutes. The stone is allowed to dry and then coated with a solution of tusch or linseed oil, which penetrates into the etched parts and makes them capable of taking ink. After about ten minutes the whole stone should be washed with turpentine or benzole, by which the etching ground is removed, when the stone is inked up like an ordinary gravure.
In this way is obtained a stone with deep etched drawing, which according to the blocking contains the titles, the rivers or roadways, and from which subsequently the necessary gravures can be taken. This stone can either be used for direct printing or it may be used as an original stone from which the necessary transfer can be made.
The same process may also be made for intaglio printing plates on zinc or copper, only then the etching must be done with nitric acid or ferric chloride.
Instead of the transfer on the light sensitive film, a drawing on transparent paper may be used, or a photographic transparency. The exposure in this case, as the opaque ink and bronze powder are not used, must be very carefully estimated.
The advantage of this process is that an intaglio printing surface may be obtained so that engraving is entirely or partially avoided, and that this printing surface may be used as an original from which the reproductions are made.
SCRAPER BOARDS, MANUFACTURED BY AUGERER & GÖSCHL, VIENNA.
No. 6.—A white scraper board printed with black lines. There are 40 black and 40 white lines to the centimetre; the ratio of black to white is as 1 : 2. At right angles to the black lines impressed lines are arranged, of which 37 are depressed and 37 raised up to the square centimetre.
No. 7.—This is practically the same as No. 6, only that the lines are slightly less in number, namely, 35 black and 35 white and 26 impressed lines in equal areas to No. 6.
No. 8.—This contains dots instead of lines, both black and impressed; there are 1,156 black dots at regular intervals, and 961 impressed dots to the square centimetre.
No. 9 is a smooth scraper board.
Nos. 10 and 11.—These are impressed with straight lines in the proportion of 1 : 1. With No. 10 there are 27 lines, in No. 11, 37 lines to the centimetre.
Nos. 12 and 13.—These are impressed with lines at right angles to one another, so that regular squares are formed. No. 11 contains 730, No. 12, 1,370 squares in every square centimetre.
