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.[Back to Contents]
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.
This first etching, on account of the short exposure, goes over the plate in about three minutes, and is simply intended to get the light tints. The plate is again cleaned off and coated, this time in a different manner, and given a much longer exposure under the positive. The next etching takes about three hours, which gives the blacks great depth. Comparing this with the transfer plate which has an etching of from fifteen to twenty minutes, the reason for the difference in the wearing qualities of the plate is quite evident. This process, whether used by myself or others, I feel free to say is the best one that has ever been worked, inasmuch as it gives a far more faithful reproduction than any of the others with a minimum of work by the retoucher.