A technical dictionary of printmaking, André Béguin.
B . INTAGLIO PRINTING.
1°) GENERAL PRINCIPLES. In intaglio printing there are other problems over and above those caused by the grain of the paper. In order for the paper to pick up the ink lying in the furrows of the plate it is essential that the paper be pushed into these furrows. This means that the paper must he very supple, elastic when packed*, and must resist great pressure. Insofar as the paper is concerned it must be as flexible as a piece of cloth which means that it must he well dampened (much more so than fur relief and planographic printing). Dampening is absolutely necessary even when using the best grade "pure rag" paper available on the market. Dampening allows the artist to avoid a high printing pressure which is always bad for engraved lines since pressure tends to clog the lines and crush the grained parts of the plate. Hence the dampening of printing paper allows for clear lines. An easy experiment demonstrates the difference between a dampened sheet and a dry one; just print two sheets (a dry one and a wet one) using an uninked plate. The damp sheet will have followed the lines and furrows of the plate and thus will show up the design perfectly whereas the dry sheet witi barely carry the design of the plate.
Paper must be dampened in function of the type of printing to be done (wetter for very delicate details than for strongly cut lines), in function of the paper (thick paper and sized paper must be immersed in water while Japan, China, and Dutch papers which react like blotting paper must be dampened with a sponge), and in function of the printing pressure.
In any case the sheets of paper must be dampened uniformly before being printed but must be damp enough to exude water when under the press. If the sheet of paper is too dry it will not "empty" the inked plate and the result wilt be white printed areas or gray lines.
A uniform dampening is most important. This might present some problems in overheated studios or in summer, especially if the sheets are large format ones. In fact, if one lets the sheet of paper shed its excess water before wiping the plate (a process that may take quite some time) the top of the sheet will be practically dry whereas the bottom will still be quite wet. The printer must therefore be careful to let the sheet drip only five to ten minutes before printing or else use the "impregnation" system described below.
2°) DAMPENING METHODS.
Basically there are two different methods for dampening paper: the immersion technique and the impregnation technique.
The immersion technique has been used for a long time in intagho engraving. Bosse described it as of the 17th century. The sheet of paper was plunged into a basin that was lust a little bigger than the sheet itself. Depending on the hardness of the paper the sheets were plunged two or three times into the water or even more often [* paper). After this wetting and "depending on the strength and the sizing of either side of the sheet" the paper was put on a wooden board next to the basin. The board was just big enough to take the sheet of paper. Each dampened sheet was placed above the preceeding one and at the end the pile was covered with another board and weighed down with a heavy object. The reason for the second board and the weight was to ensure both a uniform dampening and the draining of excess water. This job was usually done the evening before printing, sometimes just before printing. The paper used for intagho printing was what the french engravers called vieux trempé. The printers of the past often put some alum into the water they used for dampening in order to make the paper stronger.
The method described above is still valid. One should wet fairly strong papers (more than 200 grams) for about 20 minutes or even a whole night (as in the case of aquatint printing). The water used must be clean and, if possible, one should use rain water. The water should be thrown away after a couple of days of use since it begins to be full of paper threads and dust. Three drops of phenophthalein or a similar product will keep the water aseptic if it must be kept for prolonged periods of time.
A prolonged immersion of the paper must be followed up by the "piling up" method described above. However, one may also let the sheet of paper drain by hanging up to drip dry just before printing on it (5 or 10 minutes before). If this is the system chosen one must hang the sheet (using tongs to grip a corner) up above the basin. As I have already mentioned one must be careful that the draining of the sheet of paper is properly done in hot water. Of course this second method is better if individual prints are made and especially if one is colour printing. The piled up technique is, on the other hand, better if one needs to print a large number of impressions of the same plate.
When a dampened sheet is handled for printing it must always be picked up with tongs in order not to dirty it. It should then be placed on a clean sheet of blotting paper and covered with yet another sheet of blotting paper in order to dry it. Then extract the damp sheet from the blotting paper and brush it with a pig bristle brush (fairly hard grade bristles are best) making sure not to brush too hard. Brushing is done in order to even out the surface of the paper and to eliminate any dust that might have accumulated. Withdraw any extraneous elements which might be incorporated in the paper and which might prejudice the results of the impression.
Immersion is done with strong and hard papers but I do not recommend the immersion of Japan, China, and Dutch paper (at least the 200 gram weights). In fact such paper is sized very little or not at all and thus absorbs too much water. When paper is well sized but light weight the quantity of water absorbed is still excessive and it is difficult to handle such sheets without ripping them. Furthermore, the drying process is much too slow or then acts like blotting paper (in other words it is uneven).
It is therefore best to dampen such types of paper by impregnation. Each sheet should be put between two sheets of damp blotting paper or else dampened with a sponge and then placed between two sheets of blotting paper.
Obviously the degree of dampness affects the size of the sheet of paper and while it dries it will also shrink. This characteristic is particularly troublesome in colour printing done by superimposition. Any shrinking that takes place will throw off the registering. Artists must, therefore, print all of the colours while the sheet is still damp. Actually what this means is that the various runs must be accomplished as fast as possible. Of course one may always repeat the dampening process since the oily inks used in printing will not he disturbed. Nevertheless such dampening only allows for approximations and it will be found that the less steps there are in printing the better [ * registering].
Industrial intaglio printing is always done on dry paper which is the reason for which the lines of such plates must be particularly precise. Dry paper is also the reason for which this process uses very fluid inks and is printed at great pressure.
2. DAMPENING OF TRANFER PAPERS.
Transfers on stone or metal are done by means of special transfer and autographic transfer papers. Autographic paper allows one to draw or write with autographic ink on a very highly sized sheet of double faced paper. One side of this paper is shiny while the other is mat. At times such paper is transparent and thus allows for tracing. Autographic transfers are used in lithographic work.
In order to transfer a design place the sized side of the sheet face down on the stone or metal plate making sure that it is property registered*. Slightly dampen the back side of the sheet with a sponge until it becomes rather mat. Then, after covering the autographic paper with a sheet of set-off* paper, press it down several times, increasing the pressure each time. Carefully lift off the support sheet, wetting the back with a sponge and pulling it up vertically.
Transfer paper is heavier and stiffer than autographic paper but on the other hand it has a grain that allows for crayon manner work. If need be one can rub out the grain. Apart from such considerations tranfer paper is used in much the same way as autographic paper. The artist draws on the sized and grained side of the sheet with a transfer ink or with a chemical crayon. The back of the sheet is then wetted in the same way as for autographic paper (but remember that it needs to be wetter). The person doing the transfer may need to wet the sheet several times over. Some people prefer to first press the paper transfer down with very little water in order to fix the oily ink to the plate. They then dampen the sheet thoroughly to remove the paper.
3. DAMPENING OF LIGHT SENSITIVE PAPERS.
Photosensitive paper carrying an image can be used to transfer this image onto another surface, usually a metal plate. At present transfers are systematically made in photogravure* but tranfers of drawings and texts can also be made. Furthermore, transfers can be used in photolithography and in various other engraving processes [ * transfer]. In the past gelatine transfer papers were used in photo-engraving and in photolithography. Today photogravure uses pigment paper [ * paper].
Gelatine tranfer sheets are inked with a roller, and since only the image receives the oily ink, the transfer is simply made by pressing the sheet onto the plate. Celatine transfers are therefore done more or less in the same way as for ordinary transfer paper. However, gelatine transfers require more careful handling. Before proceeding put the gelatine sheet into a pile of paper of which every third sheet has been dampened with a sponge. The pile must have been prepared 24 hours beforehand so that the dampness will be uniformly distributed. Leave the gelatine sheet in this pile until it begins to become sticky. Then proceed as with normal transfer paper. The pressure used to transfer the ink onto the stone or plate should be sufficient to avoid dampening the paper any further. A second dampening will, however, be necessary if the ink has dried too much. If this is the case dampen the back side of the gelatine sheet with a sponge and pass the sheet through the press a second time, using a greater pressure.
In order to separate the gelatine sheet from the stone or plate wet it on its back with a sponge and pull the sheet off gently, being careful not to damage the transfer.
In photogravure the dampening of pigment papers is usually done to ensure the suppleness of such paper. In fact, when such paper is new it contains about 10% of its weight in water. If the atmosphere is too dry the paper becomes hard and brittle. Because of this one must put it in a very damp place (60% humidity) for several hours before using it. Check that the humidity is correct by using a hygrometer. Dampening may be done by hanging sheets or rolls of such paper in a metal cabinet along with some wet rags. Pigment paper must be dampened a second time once it has been exposed and the pigment layer is tranferred to the metal plate. This second dampening is carried out in order to detach the gelatine from its paper support.
If its dimensions are not too big the entire plate can be plunged into a basin full of clean water. Then immerse the paper, face up, until it has rolted up. Once it has rolled up turn the paper face down and apply it to the plate, making sure that the sheet is placed correctly on the plate. Remove the plate from the basin, put it on a table and put pressure on the pigment paper with a rubber squeegee. Sponge the result and leave it for some twenty minutes before removing the paper. If the transfer must be made onto a cylinder it will not be possible to do this under water and since the wetting of a large sheet of gelatine would make the sheet swell unevenly one must add some alcohol to the water (as much as 50%). For cylinder transfers the paper is immersed alone and then applied to the cylinder. Pigment paper can, however, also be applied, when dry, to a copper surface by fixing one side of the sheet to the copper cylinder (by means of tape) and then plunging the cylinder into water. The contact between the dry sheet and the wet cylinder will be enough to ensure the transfer. Apply pressure and force the gelatine to stick to the cylinder [* photogravure].