Page images
PDF
EPUB
[graphic][merged small]

Three-Colour Process

D
SHOWING THE SEPARATE COLOURS EMPLOYED IN PHOTO-REPRODUCTION BY THE THREE-COLOUR PROCESS
The three primary colours are separated out by photography, each colour sensation is etched on copper, and when the blocks representing Yellow (A), Red (B), and

Blue (C), as illustrated above, are superimposed in the printing press, the result (D) is a reproduction of the original in all its combinations of colour

[graphic]

the attempts that were being made to reproduce his work ink, or ink that will tell as black when it is exposed to the phctomechanically without the intervention of the translator or graphic plate. Inks of a warm lone—that is, inclining to red interpreter. The ideal of an artist would naturally be a repro- or orange-yield better results than cold inks which incline to duction of his work in facsimile, which retained all, or as many | blue. as possible of the individual characteristics of his work; and

Most prepared liquid inks have a tendency to lose their blackness to give him this was the aim of the school of wood engravers by exposure to the atmosphere on the removal of the cork from which originated in the United States and made a last stand to the bottle. The ideal ink is one freshly ground from a dry cake of

colour when beginning work. Indian ink is good is well ground and maintain the position of their art in the field of book illustration.

kept sufficiently thick to assure the necessary blackness. It has By a system of extremely fine work the American wood engravers

the advantage of not washing up when colour in washes is passed were able to keep much closer to the tones of an original than had over it, but it must be used freshly ground. The addition of a little previously been possible; but the result was obtained at the Indian yellow, burnt sienna or sepia, gives a warmth of tone to it

and renders it photographically more active. Bourgeois ink, sacrifice of the artistic rendering of the best old engravings, and

prepared by Bourgeois of Paris, appears to be prepared with the was so mechanical in its character that when it had to compete

admixture of some warm colour with the black base. It is a good ink with a real mechanical process the engraving could not hold | for the purpose, and is prepared both in solid and liquid form. its ground, the enormous difference in the cost of production Lampblack gives good black lines; so does ivory black, which is

warmer in tone than lampblack. Higgins' Indian ink or American being a factor of sufficient importance in itself to make it im

drawing ink is an American ink made in liquid form which has the possible for the engraving to retain the field. A similar develop

reputation of not fading by exposure. Stephens's Ebony Stain is ment had been going on in the other branches of engraving. a fine black medium which does not clog the pen; if it thickens and The line engraver and the etcher, to whom had been entrusted dries, it cracks off and does not corrode the pen. the interpreting of works of art first produced in other forms, Besides the pen a brush brought to a fine point is much prefound themselves faced by mechanical reproductions in plate ferred by some artists, as it yields a line less monotonous than form which, while preserving more of the character of the original that given by a pen, though the brush cannot be used so freely. work, were produced in much less time and at a greatly reduced | The paper used should be smooth and as white as possible. A cost. It has thus come about that the last quarter of the 19th paper is made with a surface coating of white chalk, which century witnessed the dispossession of the hand engraver from admits of the use of a scraper to remove lines or to break the field of interpretative engraving, and the occupation of his them up. position by the chemist and the mechanician.

It is not possible to lay down a rule for the amount of reduction The term "process," which has come to be applied to all to be made when photographing for the reproduction; the finer photo-mechanical reproductions, is a somewhat unfortunate the drawing the less should be the reduction made; but expcone, inasmuch as it is descriptive of nothing. From time to rience is the only guide. Sometimes, where the lines time various names have been given to its varying forms, indica- fine and the drawing minute in character, an enlargement is tive either of the name of the inventor or of some peculiarity desirable. Where drawings are reduced too much, there is of method. Zincography, gillotype, photogravure, heliogra | a tendency for the spaces between the lines to fill up, and to vure, heliotype, phototype, albertype, are illustrations of the give a coarse, heavy result. Faulty drawing is not lessened kind of name given osten to very slightly varying applications by reduction. On the contrary, the fault becomes more evident, of the same principle, but usage has come to apply the term so it is desirable to make all necessary corrections in the drawing. “ process ” to any printing surface that is produced by chemical

| The original drawing which has to be reproduced is photoand mechanical means. The whole of these processes may be graphed to the size of the required block. The negat arranged under three heads: (1) relief; (2) intaglio; (3) plano is absolutely dense except where the lines of the drawing have graphic.

affected it, and these are absolutely clear, admitting the unre1. Relief Processes.-An engraving in relief is one in which

stricted passage of light through them. A picce of planished the printing surface stands up above the surrounding ground.

copper or zinc is prepared or made sensitive to light by a preThe history of the development of relief processes is really the

paration of albumen or gelatin and bichromate of potash history of photography (9.0.); for whilst attempts were made to

spread upon its surface. The negative is laid upon the sensiobtain results without the aid of photography, by drawing upon tized metal and placed in the light in the way an ordinary photoplates with prepared chalk or ink, “rolling them up ” with graph is printed. The light passes through the transparent printer's ink and etching away the ground with acid, as in the lines of the negative and hardens the bichromated film beneath case of zincography, the real progress of all process has been them. Both negative and plate are then taken into a darkened upon the lines of photography; and to Niepce and Daguerre

room, where the metal plate is rolled with an inked roller, may be attributed the origin of the modern mechanical and placed in a bath of cold water and allowed to soak until the chemical processes.

albumen and bichromate becomes so softened everywhere, Speaking broadly, all the modern “processes” are the out- except where the light has hardened them, that they all wash come of a discovery by Mungo Ponton that a preparation of away, and nothing is left but the hardened lines. The lincs albumen or other colloid substance and bichromate of potash are dusted with asphalt, which by heat is melted on to them, could be hardened and rendered insoluble and nonabsorbent in and makes a ground which resists the action of acid. A coat water by exposure to light, and that as a photographic negative of varnish is put over the back and edges of the plate, to protect permitted the passage through it of light in varying degrees them from the acid also, and only the spaces between the lines of intensity, so a film of the preparation placed under a negative

on the surface are left free to its action. The plate is then placed was liable to be hardened and rendered insoluble in degrees in a bath of dilute nitric acid, which cats away the metal wherevarying with the intensity of the light affecting it. This dis- ever it is exposed; but it leaves the lines of the drawing, which covery governs the production of process blocks or plates of all are protected by the hardened film standing up above the eaten kinds.

or etched surface; and these lines, which correspond to those The methods of reproduction of pure line work differ greatly of a wood engraving, are the printing surface of the plate. The from those for the reproduction of originals in tone. As the

plate is mounted on a wood or metal block, made type-high, first necessity in securing a good result is the suitLlao

and it can then be used along with type in the printing-press. ability of the original to be reproduced, it is desirable Blocks.

Various devices have been resorted to that effects of tone may to make clear the character of a good original.

be obtained by means of the simple line process. Grained papers This should be of one tone or degree of colour all through. It with a surface of chalk, upon which are printed close-ruled lines may be all grev: it is better that it be all black. It may not | crossing at right angles, or rows of dots give the papers a heavy, be black in parts only and grey in others. The lines of an original

flat, "tone," upon which a drawing can be made in pencil, chalk

or ink, and gradations of tone introduced by means of scrapers, may be of any variety of thickness. It is necessary, therefore, which remove partially or entirely the black ruled lines or dots, for the draughtsman to see that he works with a good black leaving, if desired, high lights of pure white. A dawing on such

paper consists of lines or dots, a combination of the original lines shall not at a glance appreciate the broken-up character of the or dots of the paper and those of the drawing itself, the scraper

surface of the block. Many efforts resulted in the production splitting up lines into dots or removing them altogether. The result is quite easily reproduced by the line process. Another

of what is known as the screen, which itself was only made method is by the use of what are known as Day's "shades," or possible by the invention of ruling machines of a delicacy shading mediums. They are transparent films of gelatin which previously unknown. have upon them lines or dots in varying combination in relief, so

A screen is made by coating a sheet of glass-which must be that they can be inked up by a roller. When placed over a drawing, their transparency enables the operator to see exactly what passage

flawless both as to body and surface with a composition he is dealing with, and he can by means of a burnisher impress the analogous to the ground used by an etcher to coat his plate lines or dots of the shade upon any passage of the drawing; these before drawing upon it with his needle. The glass so coated lines or dots then become part of the drawing; and are reproduced

is placed in an automatic ruling machine, of which the ruling in the usual way.

Pencil or chalk drawings upon simple white-grained paper, where point is a diamond, and which can be adjusted so as to rule any the pencil or chalk passing over the ruts or hollows in the paper number of lines from 50 to 300 to the inch. The lines are ruled makes a mark on the top of the grain only, are also reproducible by diagonally on the glass, and at mathematically equal distances the line process, but such drawings are apt to be unequal in colour from each other. The sheet of glass. after ruling is treated with and difficult to deal with. The difficulty led to the invention of a process by Henry Matheson, who not having the capital to work it. hydrofluoric acid, and the lines where the ground is cleared joined the late Mr Dawson, senior, whose sons continued to work away by the diamond point are etched or bitten into it. The the process with Matheson under the name of the Swelled Gelatin plate is cleaned up and an opaque dark pigment rubbed into the

Process. It is based upon the fact that gelatin, sensiSwelled

lines. Two such ruled sheets of glass are sealed together face tized with bichromate of potash, swells when placed in Gelatia water, and swells in proportion to the amount of light

of light to face with Canada balsam, with the diagonally ruled lines, Process.

to which it has been exposed. A negative taken from crossing each other at right angles, the result being a grating or a drawing which varies in tone, not being thoroughly black all screen containing innumerable little squares of clear glass through, varies in the quality of its transparent lines and dots; l through which the light can pass, which it cannot do through and when a piece of paper or glass coated with sensitized gelatin is exposed to the action of such a negative it is affected according

the ruled lines, which are filled by the opaque pigment. to the amount of light the negative allows to pass. After making To produce a half-tone block from a picture, a black and a print on such paper or glass, it is placed in a dislı of water and white drawing in tone, or a photograph, a negative is exposed the surface allowed to swell, which it does in varying degrecs, the l in the camera in the usual way, with this screen quite close to it portion unaffected by the light absorbing most water and swelling most. the hardened lines of the drawing not swelling at all. This but not in contact; and the subject is photographed on to the swelled print is then placed in a frame, and a preparation of plaster negative through the screen, and what is termed a "screen is poured upon it to make a mould of its surface. When this has negative" is the result. It is a photograph of so much of the set and the gelatin has been removed, this mould is filled with a

original as could affect the negative through the little clear preparation of wax, which sets in a few minutes sufficiently for it to be released from its plaster mould. Additional wax is built

squares of the screen, and represents the tones of it by inup when necessary upon the "whites," as they are technically numerable dots and lines, the size and proximity of which are called that is, the passages which represent what will be the regulated by the fineness or coarseness of the screen used. hollows in the block--so that these may be as deep as possible, and

In the early days zinc was the metal used for these ball-tone this wax mould is electrotyped in copper. The lines and dots of this copper block, which when finished is backed up with metal and

blocks; but experience showed that though more difficult to etch mounted, vary slightly in height, the result being that the slightly to the necessary depth, the closer, denser texture of copper lower dots do not come so closely in contact with the inking roller or rendered plates of this metal much more suitable for the produce with the paper, and so produce when printed a grey impression

tion of the best blocks, and zinc now is used only for inferior corresponding to the greyness of the original drawing The drawback to the use of the process is that it is about three

blocks. Whichever metal may be used, a sheet of it, most times as costly as the ordinary process. It is a method much used carefully planished, is sensitized with a coating of gelatin or for the reproduction of line and stipple engravings, where fine fish-glue and bichromate of potash, dried and exposed under dots and lines are apt to be printed in delicate tones. The finest

| the screen negative to the action of light, as in the ordinary

the results by this method are producible, however, by omitting the plaster mould and wax-cast stages, and by coating the sensitized method of photographic printing. The action of the light gelatin with plumbago or other impalpable metal preparation which hardens the gelatin film, the portion not so hardened being will enable it to receive a copper deposit to qualify it to take its

soluble by water. The plate with the gelatin picture in lines place in the electrotyper's bath, and so to get the needed thin coating

8 and dots is exposed to heat and the image is burnt in on the of copper from the surface of the gelatin itsell; but this needs to be done with the greatest care, and is still more costly.

surface of the metal like an enamel, which enables the photoA non-photographic process of obtaining line blocks in relief has graphic picture to resist the subsequent etching. The plate is been for a long time successfully worked by Messrs Dawson. A placed in a bath of iron perchloride and etched until sufficient

.. brass plate is coated with a film or ground of wax upon depth is obtained. Wherever the surface of the plate is free Typographic which a tracing of the drawing to be reproduced may Etching. be rubbed down. By means of an etching needle the from the lines and dots, it is bitten away by the perchloride, lines of the drawings are incised upon the thin wax ground down and the lines and dots are left in relief. This first biting in the to the surface of the brass plate. A pencil of wax and a pencil of bath produces a rather flat general impression of the original, hot metal are then used to produce a flow of melted wax which drops from the wax pencil upon the ridges of wax between the lines and

and is termed “rough etching." To produce finer results, and builds them up until they are of sufficient height. The risk that to bring out the contrasts of black and white necessary to a good this wax may run into the incised lines has to be carefully guarded reproduction, the block has to go through processes of stopping against, but 'skilful treatment manages so that it stops at the edges out and rebiting similar to those of etching an intaglio plate. and does not run over. In maps and diagrams where lettering or This “ fine etching" calls for the artistic taste and judgment of figures are necessary, type is impressed into the wax with a very neat and precise result. By this means a mould is formed, an the craftsman; and with a good photograph to work electrotype from which gives a really good relief block which may final quality of a block will depend largely upon its treatbe printed with type.

ment by the fine etcher. A substitute for the acid bath has been

found in an acid blast. The acid is driven in the form of a The invention of line processes only stimulated the efforts spray with some force on to the surface of the prepared plate, to find out some means w to find out some means whereby tones might be reproduced on which it etches more rapidly and more effectively than the

: blocks or plates that could be printed along with bath.
Hall-tone
Processes.

type in the ordinary rapid printing-press.
Type 1

It is One risk to be guarded against is the underbiting of the lines only possible to approximate to the printing of a flat and dots which form the printing surface. As soon as the acid or graduated tone by producing a broken or granulated has eaten its way downwards past the protecting surface film, it surface which shall present a series of lines or dots that, when will attack the sides of the upstanding dots as well as the ground inked and impressed upon paper, shall by the variations of that supports them, with the result that they become weakened proximity and size give the impression of an unbroken tone. and rendered liable to break off in the process of printing, as This necessitates the lines or dots being so small that the eye l well as to make the obtaining of electrotypes from the blocks a

matter of extreme difficulty, the underbitten points breaking These records are coloured photographs; they are simply or tearing away in the mould. To avoid this underbiting a ordinary negatives, records of colour values which may be fatty ground is laid over the surface of the block each time it is translated into colour by the use of coloured inks. The principle etched; by exposure to heat this ground is sufficiently melted governing the process is analysis or separation followed by to permit of its running down the sides of the upstanding points, recombination. Positives are made from these colour records, and so giving them the required protection. The acid blast is from which by means of the rule screens already described less liable than the bath process to eat away the sides of the dots. half-tone process blocks are made which, when printed one over

This method of making tone relief blocks is most generally the other in coloured inks, combine again the colours which were known as the “Meisenbach" process, from Meisenbach, of separated by the filtering process and give approximately a Munich, who was the first to make it commercially successful, reproduction of the original in its true colours. The colour but the history of its development is somewhat obscure. Fox used with each block must have a relation to the filter used in its Talbot as early as 1852 took out a patent for using a screen of production. It must represent a combination of the two colours crape or muslin; he also suggested dusting glass with a fine stopped out by the filter when making the nega powder to produce a grain screen. All the early ruled screens the block was made, that is to say, the colour used must be were single line, and the credit is due of suggesting the shifting complementary to the colours stopped out. Certain subjects of the single line screen during the operation and, by reversing it, which are amenable to long exposures can be dealt with by producing the effect of the double line, to Sir Joseph Swan, who what is known as the “ direct process," whereby the screen patented the process in 1879. Meisenbach's patent for a similar negative and the colour record are made by one operation on method is dated 1882. The development of the screen was the the same plate. By this means six of the fifteen otherwise important factor in the development of the process.

ment of the process. The necessary operations are saved, but the method is not always early screens were photographs of ruled plates and the great practicable advance was made by Max Levy of Philadelphia, who made it As far back as 1861 the suggestion was made at the Royal possible by his ruling machines to produce screens of a fineness Institution by Clerk Maxwell to reproduce objects in their and clearness not previously practicable. It was F. E. Ives natural colours by superimposing the three primary colours.. who, in 1886, introduced ruled screens placed face to face and Later Baron Ransomut, of Vienna, Mr Collen, a gentleman who sealed up so as to produce cross-lined screens.

taught drawing to Queen Victoria, and two Frenchmen, MM. The chief objection to this process is its inability to reproduce Chas. Cros and Ducos du Hauron, carried on the idea and the extremes of expression employed by the artist in black and made experiments with the aid of photography, which were white; actual white is impossible, and delicate tones, such as still further developed in Germany by Professor Husnik, of are characteristic of skies, are destroyed by the cross-bar lines Prague, Dr Vogel, of Berlin, and others; but it was in America of the screen, which cover down all light passages and rob the that the first three-colour blocks for letterpress printing were reproduction of that brilliancy which characterized wood made, F. E. Ives, at Philadelphia, being their maker in 1881. engraving. It is true that the addition of hand engraving can This three-colour relief process has made great advances in be resorted to in the case of the process block, and lights and recent years. The first great practical difficulty which had to other varieties of tone and form introduced, but this can on be overcome was to produce three screen blocks which could be done on blocks of very fine texture, and the cost of reproduc- be printed one over the other. Were the screens of each block tion is greatly increased by the introduction of such handwork used at the same angle, the lines and dots would print on the by the engraver.

top of one another; but a great deal of the colour result depends The most important development of the half-tone process upon a considerable proportion of each colour being on the is in the direction of the reproduction of works in colour by means | white paper. Artists know well that much purer and more Three of relief blocks. The theories of colour (q.o.) in brilliant results are produced by placing touches of colour side Colour light and in pigments enter largely into this develop- by side than one over another; small patches of red a Blocks. ment. White or solar light is composed of rays of placed side by side, yield to the eye a purple of much greater light of three distinct colours, red, green and violet, which are purity and beauty than the same touches of colour worked one called the primary or fundamental colours because by their over the other. Consequently it was found necessary to turn combination in various proportions all other tones of colour the screen at a different angle for each block, so that the lines are produced, but they cannot themselves be produced by any should not fall on each other but should cross each other; but combination of other coloured rays. The theory of pigmental the risk of this is that, used at certain angles, the crossing of the colour differs from this in that the primary or foundation colours screen lines will produce what is known as the moiré antique from which all others are produced, while being themselves result. Vogel took out a patent in Gre unproducible by any admixture, are blue, red and yellow, and and he therein stated that the screens should be used at certain while the combination of the red, green and violet of the scientist stated angles. He also proposed to use single-line screens, produces white, the combination of the primaries of pigments in similar to those used by F. E. Ives at Philadelphia, instead of their full strength produces black.

cross-line; but it has since been found that the cross- or doubleColour is the result of the absorption and reflection of the rays line screens can be used successfully; and that the angle at of light which strike upon a body. The rays which are reflected which they can be used is not a fixed one. are those which affect the vision and produce the sense of colour. Should the object absorb all the rays it appears black, should it

Filters are made in a dry or wet form. The dry filter is made by

spreading a film of gelatin or collodion, tinted by an aniline colour, absorb none but reflect all it is white, and between these two

upon a piece of glass. The wet filter is a cell or extremes lie an infinite variety of tones. Filters have been made trough made of two sheets of glass, sealed all round Colour which absorb and retuse passage to certain coloured rays, while and filled with water tinted with an aniline dye or

Futers.

" permitting the passage of others, e.g. a photographic filter of a

colour. The accuracy of the tint of the colour-filter may be tested

by the spectroscope, or by an instrument invented by Sir William certain colour will absorb and stop the passage of red and green | Abney, and known as the Abney colour sensitometer. This is a rays, while permitting the passage through it of the violet. theoretical test. The practical test is by photographing through It will then be perceived how, when a picture or other coloured them patches of blue, red, and yellow. If, for example, the filter object is placed before a camera, with one of these filters between

for blue records the full strength of blue with the full strength of the

colour of the legative, while giving slight or no record at all of the it and the exposed negative, the rays of light of the colour

red and yellow, it is practically a true filter. It is possible to treat which can pass through the filter to the negative will be the only the negatives themselves so as to render them more sensitive to ones which can affect it, and that it is possible in this way to the special colour they are intended to record. Indeed Dr Albert.

of Munich, has produced a collodion emulsion which is so sensitized secure on three separate negatives a record of the green, red

that the various colour sensations are directly obtained without

: and violet rays which are reflected from its coloured surf

the interposition of a colour filter. Dillerent makes of plates any object placed before tbe camera."

I demand different colour-filters. (For colour-hlter making see Ives.

Photographic Journal, vol. xx. No. 11. The preparation of these plate. Over this prepared surface is laid the film of bichromacolour-filters calls for great perfection of quality in the materials em- ftized gelatin, upon which is printed the subject through a glass ployed, and great accuracy in the using of them. The glass, whether for the dry or wet filter, must be absolutely flat as to its surface, positive; the usual hardening process takes place by the action and its two sides must be absolutely parallel. In the wet filter the of light, followed by a washing out of the unhardened portions of glasses forming the sides of the cell or trough must be parallel to the gelatin. The plate is exposed to the action of ferric chloride, each other.

which attacks it most strongly in the least exposed parts, Coloured glass is sometimes used in combination with the tinted collodion, but there is no particular advantage in this, because two but which cannot eat it away in broad flat masses of dark, even glasses are always used in the making of a filter, and each one may, in the non-exposed portions, owing to the existence of the if desired, be coated with different dyes and afterwards cemented bitumen granulation. which ensures the keeping of a grained together with Canada balsam.

surface even in the darkest passages. The following dyes or their equivalents form a basis for nearly all three-colour filters:

Photogravure is a costly process to employ for illustration.

The plates have to be printed slowly, with much hand work, as For the red printing negative } Brilliant yellow. S Brilliant green.

in the case of etchings. It is the printing that makes its use

expensive, rather than the making of the plates; and as cach Cochincal red. ... blue Brilliant yellow.

plate must be printed separately and on special paper, it cannot Methyl violet.

be employed with type, like relief blocks. , yellow , , Naphthol green.

There is much uncertainty about the production of plates by

the photogravure method; and although great improvements The first dye named is the base colour in each case, the second is have been made in the process, it is often necessary to produce employed in small proportions to produce the required modification

several plates before a satisfactory one is obtained. In all these of tint.

The theory of the three-colour process is that the same three reproductive processes the more artistic the workman the better colours shall be used for the printing of every subject; and there is the result; this is especially true of photogravure, in which the no doubt that if the filtration were perfect and the printing inks aim is to come very much nearer to the original work of the absolutely pure, the theory would work out fairly correctly in

artist designer than in the less perfect processes. practice; but there is room for improvement in both these matters, and it is therefore often found desirable to print special subjects The method of Rousillon, which was adopted by Goupil with special pigments, which makes it difficult to print several in the production of photogravure plates in the early days of subjects together. Special care is called for on the part of the the process, was to prepare the surface of the plate with a secret

printer. There must be the most perfect register of Need of

preparation of certain salts, which crystallized under the action the three subjects, otherwise a blurred effect results: Careful

there must be constant watchfulness to see that of light, so that when exposed under the negative the surface

on there is no excess of ink of any one colour, or the was broken up by this crystallization more or less, according to whole scheme of colour will be destroyed. This three-colour the amount of light the negative permitted to reach it. The process has been a rather long time in establishing itself and nothing

plate with its crystallized surface was then electrotyped, and the has so tended to retard it as bad printing. Good blocks have been obtainable, but in the hands of ordinary printers they have yielded electrotype was the plate used for printing. It was a deposit but indifierent results. It is hardly to be expected that the untrained process, as opposed to an etching process. eye of the ordinary printer should be successful where the work

Photogravure plates are made also by the use of the grain requires the cultivated judgment of an artist. There is one other

screen, in which the reticulations of the screen take the place necessity for success in all tone relief work, and that is the use of the right quality of paper and ink. The blocks are so delicate of the bitumen powder in producing a grain; it is the inversion they soon fill up if an excess of ink is used. Ink of a good quality of the method by means of which points and lines are produced can be used in much less quantity than common kinds, but it must in the relief block. It has not, however, come much into favour, be impressed upon paper that is sympathetic and will "bear out" the ink.

probably owing to the greater coarseness of the grain and the The best results can be obtained only with the use of what is consequent loss of softness in the tones. An application of known as "coated " paper. It is a paper which, after manufacture, this method has, however, been made in the development is passed through a bath of a preparation of china clay, which by known as the Rembrandt intaglio process. It is a secret means of brushes is rubbed into the surface of the paper. When

process; but the secret lies more in the press by which Rembrandt dry the surface takes a high polish, and is sensitive to the smallest amount of ink. The polish of this coated paper is objectionable the plates are printed than in the plates themselves, lataglio to many readers of illustrated books, and the clay adds considerably which are intaglio plates made with a very fine screen Process. to the weight. Paper makers are, however, supplying a dull

and bent to a cylinder. The attempt to print photogravure surfaced highly calendered rag paper which is very good lor artistic and scientific illustrations and obviates both the glossy surface and

plates by machinery was given up because the plates were so the supposed lack of permanency of chromo paper.

shallow they would not stand the wear and tear, and their life

was too short and the results too indifferent; but the use of the 2. Intaglio Processes. An intaglio engraving is one in which grain screen renders possible stronger, decper plates, that will the printing surface is sunk below the surrounding portions of stand harder wear. There is little doubt that the machine used the plate; the lines or dots--pressed, cut or bitten into the surface is some form of the machine used to print wall-papers, in which ---holding the ink which is to be impressed upon the paper when there is a central cylinder engraved with the design, inked by the original surface of the plate is wiped clean. The old- rollers with which it comes in contact.

rollers with

The ink not only fills fashioned steel engraving may be taken as the type of an intaglio up the intaglio or sunk portion which has to print the design, plate, in which the lines which printed were cut into the surface but covers as well the whole surface of the plate. To clean this of the plate, instead of being left standing up in relief, as in the surface, leaving ink only in the sunk dots and lines, another case of a wood cngraving.

metal cylinder is employed, ground and grooved somewhat like “ Photogravure " is the name by which the many processes the shaft of the common steel of the dinner table used to sharpen are generally known by means of which intaglio engravings knives, the grooved surface of which, passing over the engraved are made mechanically, “ heliogravure" being another name for cylinder, scrapes clean its inked surface, leaving ink only in the the process, or special application of it. Photogravure repro- sunk portions, which will, as the cylinder comes in contact with duces the tones of photographs or drawings, and gives the the paper, deposit itself and print the picture. The results ncarest approach to a facsimile reproduction that has yet been produced by the Rembrandt intaglio process are softer and arrived at. Gelatin bichromatized is the medium by means of smoother than those given by photogravure, and they are free which the photogravure plate is produced, but as the screen is not from the gritty qualities which occasionally characterize photoused in ordinary work, it is necessary to produce an ink-holding gravure; but they lack the brilliancy and depth of the latter. grain in some way upon the plate. This is done by allowing a The process on the whole is less costly to use, mainly because cloud of bitumen dust, raised inside a box, to settle upon the the printing is so much more rapid, and is turned out by a surface of a copper plate; it is fixed by heat, which, though machine instead of by hand. insufficient to melt it, is enough to attach the fine grains to the A method of printing intaglio plates made from a screen

« PreviousContinue »