Part 16

To make a half-tone plate of a photograph or other subject, it is necessary to break the negative up into lines and dots. It is for this purpose that the half-tone "screen" is used. The screen consists of two thin pieces of plate-glass, on the surface of which a series of very delicate parallel black lines have been ruled running diagonally across the glass. When these pieces of glass are placed together, face to face, the parallel lines ruled on them intersect each other at right angles, giving a very fine "mosquito-netting" effect. The method of making the negative is very similar to that described in making line negatives, excepting that in making a half-tone negative the screen is placed in the plate-holder directly in front of the negative. The subject is then photographed, and the result is a negative completely covered with a mass of fine transparent lines and dots.

Copper is generally used instead of zinc in making half-tone plates. In making a print on copper the light shines through the transparent lines and dots of the negative and hardens the sensitized surface of the plate. The black parts of the negative between the transparent lines and dots protect the sensitized surface. When the plate, after printing, is placed under a water tap, the parts of the sensitized surface that have not been acted upon by light wash away, leaving a print that becomes acid proof after being subjected to an intense heat.

The method of etching a copper plate is similar to that already described for etching zinc plates, excepting that sesquichloride of iron is used instead of nitric acid. In a half-tone the dots and lines are so close together that great depth is neither desirable nor possible, and no steps are taken to prevent undercutting.

The half-tone plate, after it has been carried as far as possible by mechanical processes, is capable of great improvement in the hands of skilful engravers. The plate as it comes from the etching bath may be termed a mechanical product. Though great skill is necessary in making the negative, the print, and the etching, the hand-finishing gives the plate many of its artistic qualities. The unfinished plate is apt to be more or less "flat" in appearance; the high lights may not be light enough, while the dark portions of the plate are apt, in cases, to be too light. The most common methods of finishing are reetching and burnishing. The finisher dips a camel's-hair brush in acid and applies it to the high-light portions of the plate, or other places that are too dark, and allows it to act on the metal until these parts of the plate are lightened sufficiently. The parts of the plate that are too light are made darker by rubbing down the surface of the plate with a tool called the burnisher. The skilful, artistic finisher has other methods at his command of making the plate reproduce as accurately and as artistically as possible the original drawing or photograph. High lights are sometimes cut out entirely, or a fine engraver's tool may be "run" between the lines; while a "wood-engraved" finish is produced by cutting, in certain portions of the plate, lines similar to those used in wood engraving.

In the price-cutting that has been going on as a result of the fierce competition that has existed among photo-engravers during the past few years, the artistic possibilities of the half-tone have been lost sight of to a certain extent. The product of the engravers is sold by the square inch, regardless of the fact that the cost of one plate may be double the cost of another plate of the same size, but from a different subject.

A point also worth remembering is that until the plate reaches the finishers' hands, it has been more or less of a mechanical product; and that the plate is made an artistic creation by the skill, care, and brains of an intelligent class of men earning from $25 to $50 a week. Those expecting "the best" at "the lowest price" can easily guess about how much of this high-priced finishing they will get when the price paid barely covers the cost of the mechanical product. Then, engravers striving for high quality in the product pay from twenty-five to fifty per cent higher wages, as a rule, than the cheap, commercial shops. But the idea of square-inch price has so generally permeated the buying public, that the larger and better shops have been compelled, to a greater or less extent, to meet the prices of their less skilful competitors. They are enabled to do this and give their customers much greater value for their money, only through better business methods, more modern facilities, and by conducting the business on a very large scale.

The screens used in making half-tones represent an enormous outlay in the large shops. A comparatively small screen costs in the neighborhood of $100. A screen 18 x 20, ruled 120 or 133 lines to the inch, costs about $500. Screens are made with different numbers of lines to the inch, from 65, for coarse, newspaper work, up to 400. The screens in general use are 65, 85, 100, 110, 120, 133, 150, 166, 175, and 200; but intermediate sizes are also used, such as 125 and 140. A screen containing 200 lines to the inch is about the finest ever used for ordinary printing purposes, though a few screens with 250, 300, and 400 lines to the inch have been made. A well-equipped photo-engraving establishment must have all these screens, and all of them in many different sizes. In the writer's shop there are fifteen cameras, all of them in constant use in the daytime and five or six of them are always in use all night. Some days the bulk of the work in the place will be a fine grade of magazine engraving calling for a 175 screen. In order to keep all the cameras at work all the time, a thing that is very important in a well-regulated place, it is necessary to have a number of 175 screens almost equal to the number of cameras. The same is true of most of the other screens in general use. Fortunately for the engraver and the consumer these screens practically last forever if carefully handled.

The greatest developments in process work during the past few years have been in the making of color plates. Beautiful results are obtained in two colors by the "duograph" or "duotone" processes, the plates being made for two printings. The three-color process aims to reproduce all colors in three printings, by using inks of red, yellow, and blue. This process is very interesting, but somewhat intricate. Primarily, the results are made possible by color separations. The aim is to take a colored subject--an oil painting, for instance--and by photographing it three times, each time through a different colored piece of glass, to divide all the colors into what are called the three primary colors--red, yellow, and blue. From each of these color separations a half-tone plate is made, and when these plates are put on the printing-press, and the impressions are printed over each other in yellow, red, and blue inks, respectively, the result is a printed picture reproducing correctly all the colors of the original subject.

While many subjects may be reproduced accurately by this process, yet the three-color process seems inadequate to give perfectly satisfactory results in all cases. Nearly all three-color process houses are now prepared to add a fourth, or key, plate, to be printed in black, in case the subject seems to need it. The three-color process has enabled many of the leading magazines to use illustrations in colors, and there is not the slightest doubt but that there is a great future for this class of work.

THE WAX PROCESS

By Robert D. Servoss.

Almost all of the maps found in text and reference books, as well as the geometrical diagrams used in mathematical and scientific works, are made by what is known as the "wax process."

This process was invented and patented by an Englishman named Palmer about 1840, shortly after the discovery of the method of making electrotype plates for printing purposes. He announced that he would furnish artists with copper plates covered with a waxlike composition on which they could make their own drawings, in a manner similar to but much simpler than the method followed by the etcher on copper. After receiving the artist's work, the plates were to be returned to Palmer, who then made an ordinary electrotype of the engraving. A circular, issued about 1841, gives the necessary instructions for engraving, and the prices for the wax-coated plates and the subsequent electrotypes, and shows many beautiful illustrations made by artists of that time. It was then called the "glyphographic process."

The process was first introduced into this country by a firm of printers in Buffalo, New York, and was used by them for several years for illustrating the United States patent office reports until it was superseded upon the introduction of photo-lithography and the subsequent adoption by the government of a uniform standard for patent drawings.

This process may be described in a general way as follows: A copper plate having a highly polished surface is first blackened by the application of a weak solution of sulphuret of potassium, or other chemical which will oxidize the copper. Then a composition, made by melting together in proper proportions, beeswax, zinc-white, and paraffin, is "flowed" over the blackened surface, producing an opaque whitish engraving ground. The thickness of the wax is varied according to the subject to be engraved, but in general should not exceed that of heavy writing paper. After it has been allowed to cool with the plate lying perfectly horizontal, the wax is smoothed down to an even thickness by a steel scraper, and the plate is then ready to receive the engraving.

Taking for an example the engraving of a map, the original copy is either photographed on the wax surface, or is transferred to it by covering the back of the copy with red chalk and tracing over every line with a steel point. The photograph, or the tracing, on the wax must not be a reversed one, as might be supposed, but should "read right." The outlines of the map are then gone over, with an engraving tool which cuts out a small channel in the wax, down to, but not into, the surface of the copper plate. The bottoms of these channels will eventually form the surface of the relief lines in the resultant electrotype plate, but now appear as dark lines against the whitish groundwork of the wax.

The engraving tools are made in different sizes, and therefore channels of varying widths at the bottoms may be cut in order to produce lines of different sizes. In cutting lines to indicate rivers,--which must be thin at the source and increase in thickness as they approach the mouth,--tools are used in graduated sizes. The first one cuts its own line of equal width for a very short distance, then another and slightly wider tool is used, the next still wider, and so on until the river line is completed. In reality a series of steps, the work is so done that the line appears to the eye to increase in width evenly and gradually from a very fine beginning to a heavy ending. The wavy lines indicating hills and mountains are made in substantially the same way. Special steel punches are pressed through the wax to the copper to show town and capital marks, and after all the lines and marks are completed, the plate is ready to receive the lettering. The name of each individual town, city, state, or river is set up in printer's type and stamped one name at a time into the wax. The type is placed in a small tool resembling a vise, which holds it in perfect alignment and on a perfect level. Tools of various shapes are used for stamping the names in straight and curved lines. It is necessary to wet the type to prevent its adhering to the wax.

The plate is then carefully compared with the original copy and after any necessary corrections have been made it is gone over by an expert operator, who cuts out any of the channels which may have been obliterated by the burr of the wax, resulting from pressing in the names.

We now have a plate in which the lines have been cut in small channels and the names stamped with type. This is a matrix, or mould, from which an electrotype of the lines now sunken in the wax may be made in high relief for printing, but the blank portions of the wax are so thin that it is first necessary to fill in all these places on the plates with wax in order to produce a sufficiently deep electrotype plate. This is done by "building up" the plate. A small hook-shaped tool, heated over a gas jet, is used to melt small pieces of wax which are run carefully around all the names and in the spaces between lines, thus filling up all these spaces with a round, smooth body of wax. From this mould an ordinary electrotype is made by the method described elsewhere in this book.

All these operations require much skill and patience at every step, but the plates produced by the wax process are always much deeper and stronger than those made by any other process.

MAKING INTAGLIO PLATES

By Elmer Latham.

The method by which a photogravure plate is produced, is probably the least understood of all of the many photo-processes of reproduction. This is chiefly on account of the difficulty of the process, which is not an easy matter to explain in detail, and also on account of the secrecy with which all plate makers guard their processes.

The reproduction of a mezzotint or line-engraved print, when made by a good photogravure process, produces in most cases a print which cannot be detected from the original. The originator of the process was probably Fox Talbot, an Englishman. The writer has seen one of his prints, made between 1855 and 1860, which was a very creditable piece of work. Dujardin of Paris took up Talbot's process, and after much modification, succeeded in developing a successful process which he is working to-day. All photogravure plate makers of the present time have more or less copied the process of Fox Talbot.

There are three different methods of making these plates known to the writer. The reader probably knows that a photogravure plate is not a relief plate, but an intaglio, and is printed on an etching-press in the same manner as an etching and requires special skill in printing on the part of the printer to produce the best results. I will give a brief explanation of the three different processes.

The first is known as the transfer process. In this process a reversed photographic negative is made from the copy, from which a positive or "transparency" is made, either by contact or in the camera. A piece of carbon paper is then coated lightly with gelatine, sensitized with bichromate of potassium and allowed to dry. The paper is then placed in contact with the positive and printed in daylight until the image is imprinted on the gelatine coating of the paper, such portions of which as have received the most exposure from the action of light becoming quite insoluble. A copper plate, cleaned so that it is free from grease, is introduced into a large box into which has been blown a very finely powdered resin, which is allowed to settle somewhat before putting in the plate. The plate is allowed to remain in the box until a fine deposit of resin has settled all over it. It is then carefully removed and heated over a gas burner until the resin adheres firmly to the plate. The resin is melted only to such a point that it forms a fine grain all over the plate, leaving interstices of bare copper between. The paper, on the gelatine surface of which the picture is printed, is now placed in a tray of warm water, and the parts of the image which have had the least exposure are thereby dissolved and washed away, the image being thus fully developed on the paper. This is placed in contact with the grained plate, which has been placed in the tray of water, and firmly squeezed in contact with the plate. The paper is stripped off, leaving the gelatine film on the copper. The plate is now removed from the tray and dried, and is then ready for etching, which is accomplished by placing the plate successively in several baths of acid of different strengths until the desired results are obtained. This process gives a shallow plate, of not great wearing quality, and, as a rule, requires a great deal of work by the engraver to bring the plate up to anything like the copy. The light tints come out very soft and smooth, but the black tones etch "flat" and lose all detail. These blacks must be put in by hand. The poor wearing qualities of these plates make them undesirable in cases where a large edition has to be printed.

The next process is the "deposited" plate used by "Goupil" of Paris, in which copper is deposited by electricity upon a swelled gelatine film which has had a grain formed upon its surface chemically or otherwise. The deposition has to be continued until the plate has acquired the necessary thickness, which takes about three weeks; and this is a long time to wait in these days, when a publisher usually expects his order executed in ten days. These plates are practically hand made. The process gives a plate that could not possibly be used without a great deal of retouching by an expert engraver. Goupil turns out a beautiful plate, due principally to his large force of engravers, one man working on a particular part of the plate, then passing it on to another who does some other portion, and so on, until the plate is finished. In this way each engraver becomes exceedingly skilful in one thing. Line engraving is reproduced by this process exceedingly well, but such plates, like the transfer process, are shallow and give out soon in the printing.

The last process that I have to deal with is the one I am working myself. In this process the plates are made in two or more etchings, according to the requirements of the subject which is to be reproduced. This method produces a plate of great depth both in the light and black tints, and on account of the small amount of hand-work required after the plate is etched, the copy is followed very closely. With a good positive and favorable conditions, quite frequently a plate is made upon which the retoucher needs to do no work at all, and a more faithful reproduction is made than by any of the other methods that I have mentioned. After a good positive is procured, the copper plate is cleaned, and a sensitized solution of gelatine is flowed over the plate, dried down, and then printed under the positive, with a short exposure. The plate is grained as in the transfer process, and is then etched.