If the printing is to be done on a hand press, a lithographic leather roller is charged with printer's ink, and the plate, which has been fastened on a suitable bed-plate in the press, is rolled up while it is still moist. Those parts of the plate which were acted upon by the light and hardened, repel the water and take up the ink, and thus all the graduating tones, up to the high lights or white parts, which have not been affected by the light, will take the ink proportionately. The white parts of the picture, where the light did not act upon the gelatine during the exposure under the negative, retain the natural property of gelatine to absorb water, and consequently repel the ink altogether.
From the foregoing it will be easy to understand that a certain degree of moisture in the plate is necessary to get a correct impression. After the leather roller, a composition roller, such as is used in typographical processes, is employed to make the ink smooth and give the fine details not obtainable from the rough surface of a leather roller. A sheet of paper is then placed upon the plate and by pressure the ink is transferred from the plate to the paper.
The printing, in former years, could only be done on hand presses; but with the introduction of improved power presses especially adapted to it the process itself has been so perfected that the finest work can be executed on them, at the same time insuring greater evenness and increased quantity of production, and also admitting the use of larger plates than would be possible on a hand press.
The prevailing impression, whenever machinery is employed to supersede hand-work, is that the production is increased to such an extent as to reduce the cost to a minimum, but in the gelatine printing process, even with the aid of power presses, the rapidity of printing is far behind the possibilities of the lithographic or typographical printing press, and the process, therefore, is only applicable to works of art, and the better grade of illustrations in literary and commercial publications.
The lesser rapidity of production and the greater cost is balanced by the quality, where this item comes into consideration; and where only small editions are required, even the cost compares favorably with other methods, as the initial cost of preparing the printing plate is small compared with the cost of photogravure or the better class of half-tone plate. It is only in cases of large editions of many thousands that the advantage of rapid printing reduces the cost of the initial expense. But fine art publications and illustrations will never be used in very large quantities, and, therefore, there is a large field for the photo-gelatine process in this country, where it is as yet so little used. In France, Germany, and Austria there are dozens of establishments which employ ten or more power presses for photo-gelatine work, while here only within the last few years has the process been sufficiently appreciated to warrant the introduction of a few steam presses; and these have to be imported from abroad at a high rate of duty, as the present demand for the presses does not make it advisable for our domestic press builders to invest in their construction, especially after an isolated attempt in that line, misguided by inexperienced and unpractical men, which turned out to be a total failure.
Notwithstanding all these difficulties and obstacles, it is a fact that the photo-gelatine process has gained ground sufficiently to indicate a prosperous future, as its products are becoming more widely known and appreciated.[Back to Contents]
LITHOGRAPHY
By Charles Wilhelms
As an embellishment to the modern book, chromo-lithographed illustrations are quite popular and in some cases absolutely necessary, being not only attractive, but conveying an accurate idea of the color as well as the form of the object illustrated. Although the illustration is nothing more than a colored print, it may be a revelation to some when they learn of the numerous details incidental to its production.
It may not be generally known, and yet of sufficient interest to the reader to state that the art of lithography, or surface printing, was invented accidentally. The inventor, Aloys Senefelder, had been engaged for years endeavoring to find some process for etching copper plates as a substitute for typographic printing plates; and the piece of stone (of a kind now known as Solenhofen lithographic stone), which eventually led him to the discovery of lithography had been used by him as a slab upon which he had been accustomed to grind his printing ink. The materials which he used for his acid-resisting mixture while etching his copper plates were beeswax, soap, and lampblack, and in selecting these materials he accidentally invented the basis for all crayons or lithographic "tusche" or inks, now used so extensively for drawing on stone. It seems that Senefelder finally became thoroughly disheartened about his etched copper plates, mainly owing to the great expense and labor connected with their production, and was about to discontinue his efforts when the idea occurred to him to experiment with the stone which he had used as an ink slab for so many months, treating it in the same manner as the copper plates.
He knew that the calcareous stone was easily affected by acid and that he could protect its surface against it by a layer of wax. After polishing the surface of the stone and coating it with a slight layer of wax, he made his drawing with a pointed tool, laying bare the surface of the stone where he desired the engraving. Then applying the acid and removing the remaining wax, he filled the etched lines with printing ink, cleaned the surface of the stone with water, and was enabled to obtain an impression on paper from it. This manner of treating a stone has been employed by vignette engravers for many years, but of late has become obsolete. The result gave encouragement to Senefelder and induced him to renew his experiments, when he was accidentally led a step farther in the direction of surface or chemical printing.