A technical dictionary of printmaking, André Béguin.

1. PRINTS AND COLOUR.
A . DEFINITION OF COLOUR PRINTS. From the very outset one must distinguish between prints which use only one colour (red, sepia, or brown for example) in varying shades and their opposites, which are the black prints on coloured paper. Both of these must also be distinguished from colour prints having black or dark lines in them and this even if such prints feature only one supplementary colour. When colour prints have several colours these may be printed by juxtaposition or by superimposition. One colour prints and black prints on coloured paper cannot really be considered fullfledged colour prints. Actually one should only consider colour prints those using several colours(including black).
The simplest type of colour print is the chiaroscuro print which uses two hues of one colour. One type of chiaroscuro print is the grisaille. In that the grisaille uses black, gray, and white it can be considered to be an extreme form of colour print since the gray in it can be considered a hue. In fact, when speaking of inks engravers consider black and white to be colours in much the same way as red or green but in finished prints the term colour does not include black and white. On the other hand one can speak of beautiful colours even in black and white prints when the tones are particullarly expressive or when the print sucessfully "reproduces" the tones and colours of a painting. This is especially true of 17th and 18th century reproductive prints. For example engravings based on paintings by Rubens (who supervised their making) are particularly concerned with colour rendition. Finally one might mention the case of heraldic engraving in which the colours of a coat of arms are rendered with traditional cross-hatching and stippling methods.
A colour print can be made quite simply by a manual colouring of a black and white print or by a stencil method. In fact one can certainly consider designs which are made exclusively with a stencil to be prints. The second type of colour print is one in which colour is achieved by using one or several plates with different inks. Two different methods exist to make this type of a print. The first uses a single plate or block which has several colours on it. The second method uses several plates each of which prints a particular colour. The single plate system is called the dolly printing system, a method which leaves the printer a certain freedom and responsability in working out solutions even though he may have a model to work from. Dolly colouring is done by applying colours to the appropriate parts of a plate or block with a rag wrapped around the index finger (hence the "dolly") or with a brush. Quite a lot of experience is required to print a large quantity of impressions with uniform results.
The second method of printing with colour uses several plates and can be done in two different ways: all the different colours can be printed successively on one sheet of paper or then one colour can be printed on each sheet to be printed before proceeding to the next colour. A special type of multiplate colour printing is one in which a plate is cut into pieces each one of which is inked with a colour and then all the pieces are reassembled for printing. Yet another method of colour printing consists in using a single plate several times in succession adding a new colour to the print with each impression run. In silkscreening it is possible to rework an image on the screen by superimposing on the first printing the colours of another design done on the same screen (after cleaning the previous design).
In colour printing the application of colours can be done in two different ways: either by juxtaposing the colours or then by superimposing them. In the first case the colours are printed one next to the other and although they may touch each other they should not overlap. Juxtaposed colours are generally solid* colours which are outlined by the borders of the shapes they occupy. On the other hand, in the superimposition method of colour printing the colours are printed so as to overlap (partial superimposition) or wholly cover each other (total superimposition). Depending on the opaqueness of each colour used various results can be obtained as the colours will merge with each other and change. The superimposition of colours allows for the most interesting combinations but it must be remembered that this type of printing is also the most difficult to carry out. When using transparent inks, the printer can use the three colour process, which is a way of reproducing all of the natural colours by using the primary colours: blue-green (cyanic blue), yellow, and magenta red. The two colour process entails the superimposition of two colours while the four colour process (also called the quadricolour process) improves on the three colour process by adding black or gray to darken the colours used (Japanese printing long used a final printing of black lines to give the image more relief).
Printing by superimposition is also the ideal technique for printing different colour values as half-tones can be obtained, if needed, by varying the amounts of ink in the areas to be nuanced. Of course colour printing with different values requires particular attention when inking the plates and as a consequence it can be a very delicate job.

B. HISTORICAL ASPECTS. The very first woodcuts were certainly meant to be printed on cloth but as of the 15th century woodcuts were also used for religious prints and playing cards. A good many of these images were coloured ones. Woodcuts were also used to print the outlines of images appearing in books which were then coloured to imitate manuscript illuminations. "In fact, colour did not appear only in isolated xylographies (where it is almost always used) but also in incunabula, which were not coloured by accident. The public was too much of a lover of coloured and decorated manuscripts either in terms of illustrations or in terms of illumination, the parisian word coined by Dante (l'onor di quell'arte - ch'alluminar è chiamata in Paragi). For a long time printed books tried to resemble manuscripts and featured "miniatures" . In the best books, especially those printed on woven paper, the woodcuts disappeared under the brush work, an insult which even Dürer was not spared" (].Laran, "L'Estampe" PUF, p.20). However, the need to fulfill on even greater demand slowly pushed the coloured woodcut aside and soon artists, publishers, and woodcut lovers realized that colour did not add anything to the beauty of the black and white woodcut. Nonetheless the colouring of prints which was often done very poorly with a limited range of water colours continued to be done on woodeuts as well as on maps, fashion plates, etc. up until the 19th century[ * card, image].
The chiaroscuro print appeared in the beginning of the 16th century. The first chiaroscuro prints, which were done in Germany, used only two blocks. The Italian Ugo da Carpi, on the other hand, increased the number of blocks used and thus increased the delicacy of the results achieved [* wood]. In the course of the 17th century two colour techniques were experimented. The first was developed by the Flemish engraver Seghers who retouched his proofs with a brush and thus obtained strange effects. The other method used may be attribued to the Dutch painter Lastman. Both of these techniques were known and appreciated by Rembrandt.
It was only in the 18th century and in particular around 1765 that Bartolozzi, in London, began to ink his plates with a dolly before printing. This technique was used in France some ten years later. However, as of the beginning of the century Jacob-Chistoph Le Blon had managed to make colour prints using several plates. At first he called his invention pastel engraving as the goal he sought was to imitate the effects of pastel work. He usually used four plates in this method and worked them with the tools used for the "manner" engraving of his time: the chalk-role used in the crayon manner, the rocker, but also the graver. His most spectacular feat was a portrait of Louis XV (a bust portrait). Colour work was then continued in the same direction but with aquatint* plates.
Le Blon was not, however, the only one to use several plates. Louis-Marin Bonnet had also perfected a process called the crayon manner by adapting it to a type of colour printing invented by Jean-Charles François and Gilles Demarteau. Le Blon is, nevertheless, considered to be the inventor of colour prints. "Due allowance being made for the two discoveries it may be said that Le Blond plays the same role in this engraving process as did Daguerre in the history of heliography* Both of them made enough progress to close the groping period of the respective techniques" (H. Delaborde, "La Gravure", p.253).
In China and Japan woodcuts have long been embellished with water colours and brushes when printed. It was around 1743 that colour printing using several blocks was begun in Japan. Some art historians attribute the invention of this technique to Masanobu (who died in 1768).
The 19th century witnessed the invention of a colour process adapted to lithography. Chromolithoqraphy* (chromo for short) was to have a considerable success before being dethroned around 1868, at least on an industrial level, by photomechanical reproduction techniques using colour selection. In fact photomechanical reproduction cane about, thanks to the fundamental work of Charles Cros and Louis Ducos du Hauron, in 1868.
The most recent invention in printmaking is silkscreening which has been used especially since the War to make bright prints with brilliant inks never before used in printmaking.
One might also point out that such a simple technique as the linocut, which had long been considered a substitute for wood, has come up with some astonishing results such as Picasso's work of 1962.

2. COLOUR PRINT PROCESSES.
A . THE GOAL. Each artist has in mind the result he wishes for even though at times it may not be perfectly conscious. At times this result has to be formulated slowly and painfully. However, after some time an artist tends to adopt a particular form or style. He will choose among the different colour processes the one which suits him best just as he will have chosen the printmaking technique best suiting him. Of course it is quite common that an artist chooses colour processes akin to the black and white techniques he has chosen but such a choice is not necessarily automatic. This is because certain techniques are not particularly linked to a colour process, as for example intaglio engraving whose severity is usually best satisfied by a black and white printing. Another reason is that an artist often develops a feeling about black and white work to such an extent that he feels reluctant to use colour. Finally, the use of colour printing is often linked with the use of a technique which is particularly favourable to it, as for example aquatint, lithography or, above all, the technique of silkscreening which allows for exceptional results insofar as colour is concerned. In short, amongst the great choice of techniques available everyone can find the most appropriate technique or a method of colour printing which gives the results he wishes to achieve with his art.
Experience helps to decide on the particular technique required on two counts: both an experimental knowledge of various techniques and a general knowledge of print work. It should be obvious that such knowledge carries with it a certain number of drawbacks: the problem of choice increases in proportion to the range of techniques envisaged and the time involved in eliminating and fixing the choice can become quite extensive.
What are the goals an artist may be trying to attain? The first and most obvious is to add colour to his print. To do this an impression of lines must be made which is usually done with black ink. Usually, however, an artist will want to go beyond this in the same sense that he will try out colours or a series of combinations achieved by juxtaposition or by superimposition.

B. THE TECHNICAL MEANS.
It is obvious that the colour characteristics of a print are heavily dependant on both the plate (or block) and the ink used. Contrasts, solid colours, light ones, thick ones, mat finish ink, brilliant colours, transparencies, etc. are all elements which make up the final effects of a technique.
If what is being sought after are opaque and solid colours it will be best to use a relief technique (wood or lino) or a lithographic technique in which the inking is done with a roller. One may, however, also use silkscreening which lends itself to thick colours with even a fairly strong relief.
If, on the other hand, light colours are needed in order to be partially or completely superimposed, aquatint or intaglio engraving are best suited for the purpose. If the effects of a coloured line are sought after then the crayon manner is best. Nevertheless it must not be forgotten that it is up to the artist himself to master the technique used and push its intrinsic qualities in order to achieve individualized results. Thus lithography, woodcuts, and silkscreening can also be used with light colours and even superimposition if the individual artist wishes to work out a solution for his purpose using these techniques.
In colour impression inked surface, thickness of inking, and ink quality must be distinguished from each other.
An inked surface can be solid (even) or granulated. In the first case the ink is spread all over the relevant parts of the plate and, with impression, it is transferred onto the print. If the inking is homogenous and even it does not allow for half tones or variations unless the surface is interrupted by white lines. Such a plate and its result can be compared to the industrial process called line block [* engraving and line]. In the case of granulated surfaces the ink layer is not uniform and varies according to the greater or lesser depth of the holes receiving the inking. The nuances depend on the irregularity of the holes both in their horizontal distribution over the plate as well as on their vertical (depth) characteristics. The industrial process most resembling it is the screened photogravure*.
A solid surface is not necessarily incompatible with a granulated one when the latter covers the former. Two solid surfaces are only compatible when juxtaposed or when using transparent inks, in which case the second ink modifies the first one. Two granulated surfaces work towards half tones and are the very principle of the three colour process.
The thickness of inking cannot be varied except within certain limits. In fact, too thin an ink will not print satisfactorily while too thick an ink will result in clogging. The printer does have some freedom to vary the final result as he can modify his inking in terms of quantity and he can modify the pressure used in printing. In silkscreening the inking is fundamental for the final outcome. The amount of ink, the spreading of it onto the screen, and the squeegee* work can be used separately or in combination to achieve considerable variety in the end result [ *inking].
The quality of the ink is, of course, all important. Ink can be prepared so as to come up with a light and liquid colour which will only nuance another colour or background. The opposite extreme is the thick and pasty ink mixture which will cover everything.
The order in which the colours can be printed must not left to chance. One should always begin with the lighter colours and end with the darker ones, particularly with the black line. Some colours, however, are very "intrusive", as for example prussian blue or madder red, and because of this some printers prefer to begin with these colours. In any case a priori decisions should be ruled out in favour of trial tests. The printer can also use a colour guide in which the colours and their possible combinations are analysed. Mixtures and superimpositions should be compared so that the best results may be obtained.
Insofar as the colours are concerned the order to be followed depends on the printing technique used and especially on the preparation the paper has undergone. In fact, if the paper is dry, it will not change size during the printing. On the other hand sheets that are printed when wet (because this makes the paper more printable) will dry and shrink (in function of how wet they were when the printing began). As colour printing requires precise registering each time a new plate and/or new colour are printed it is obvious that if the sheet dries between one colour and the next the registering will be off. There are three possible solutions to this problem. Firstly, if the paper is dry the first colour may be printed and then followed up by the second colour. Secondly, if the paper is only slightly damp (as is the case in lithography) a system can be found to keep the sheets that have been printed with the first colour at approximately the same degree of dampness until they are printed with the other colours. The third possibility is that the paper be soaked and the printing done on it when it is still quite wet and supple. In this third case the sheet will have to be printed successively with all of the colours until completed. If, however, the registering need not be perfect one may redampen the sheet (the oily inks currently in use are not water sensitive) in order to get it to the approximate size it had when first printed. If necessary one can always cut the second plate slightly if it turns out to be larger than the plate mark left by the first one.
Printing all of the colours of a print before moving on to the next one calls for a certain amount of organization because it is essential that the inks be neither mixed nor dirtied with each other. In summer when it is very hot one must work quickly, especially when printing large formats whose printing time can be quite long. This type of printing presents another slight drawback; the colours do not have the time to dry and consequently are a bit "fragile" which means that when the paper is passed through the press again the first colour will be picked up by the un-inked parts of the second plate. Despite this draw-back it will he found that this method can produce some very fine results [* dampening of paper].
Insofar as the superimposition of colours is concerned the reader may turn to registering.
There are various ways of registering a first run sheet to prepare it for the second run. All of them are rather delicate, the most difficult being those used to print intaglio work.
Each plate which is used for colour printing is made by a transfer* method. The first plate is printed onto a sheet of paper which, while still wet, is printed onto a second, third, or fourth plate which are worked upon using a counterproof* (drawing of the first plate in the same direction of the plate). By using such transfer means artists can try all possible combinations of juxtaposition and superimposition.
In silkscreening manual transferring is done with transparencies. In lithography, on the other hand, the use of transfer paper allows the artist to work the colour on the stone and the following colour on paper and later transfer them by pressure onto another stone (or on to aluminium or zinc plates). [transfer]
Finally, as we have already seen, it is possible to avoid transfers onto other plates by working directly on the original plate or screen. This can be done after having printed the necessary amount of impressions (before proceeding to rework the plate) or by cutting various portions of the plate which are to receive different colours and then putting them together again.