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had before 1870 become a thing of the past, while Niépce's method, further developed and improved by his cousin, Niépce de St. Victor, about 1850, came gradually into extensive use and remains so to this day, and the photo-engraving processes based on Ponton's discovery have become universally applied.
Not until over ten years after that discovery was any notable effort made to develop its possibilities and then only in some modifications of Ponton's method of obtaining chromate prints on paper, by Becquerel in 1840 and Robert Hunt in 1843. Then again nothing was done with it for another nine years, but this time a long step forward was made by Fox Talbot, an English physicist, who had early devoted his efforts to researches in this field and had worked out a method of photography on . paper sensitized with silver chloride. Talbot's experiments, following the direction of Ponton's work, led to the discovery that gelatine sensitized with bichromate of potash, when exposed to the action of light, became insoluble. Availing himself of this peculiarity, Talbot worked out a process of photo-engraving in intaglio and obtained a patent for it in October, 1854. The process consisted in flowing on the polished surface of a steel plate a solution of bichromated gelatine, letting this dry in the form of a thin film, exposing it to sunlight through a transparent positive, then washing out the unreduced bichromate with water and finally etching the plate through the unaffected portion of the film with chloride of platinum or of iron. Talbot conceived the idea of producing the effect of halftones by breaking them up into minute subdivisions of the engraving. This result he obtained by first exposing his sensitized plate under a screen of fine network, such as a piece of gauze, and then under a transparent positive of his subject, or, as an alternative, placing the screen between the positive and the sensitized plate and exposing them together. Talbot's intaglio etchings pointed the way to the subsequently developed process known as photogravure, and his application of the screen of gauze was the beginning of the halftone process. In his patent specifications he noted that the process could be applied for the production of photo-lithographs and of relief etchings on zinc, and called attention to the fact that even the thin film of gelatine on his steel plates, when immersed in water to wash out the unreduced bichromate, swelled sufficiently in the unexposed portions to produce a considerable effect of relief. Altogether, with the exception of special uses of the asphaltum process, Talbot's combination of the bichromate sensitizer with a gelatinous substance became the starting-point of all the modern photoreproductive processes. The number of these, in their various modifications, has become legion, and still more numerous are the names by which they are sought to be identified. Even for the category in general several terms have come into use, such as photo-mechanical, photo-chemical, photo-reproductive arts, etc. The distinguishing feature of all these methods of graphic representation is that the skill of the worker plays only a directive part, the creative work being accomplished by the unconscious forces of nature through the application of scientific technology. It may therefore be permitted, if only for the sake of brevity, to denominate these methods of pictorial representation as the Techno- . graphic Arts.
The development of these arts on the basis of chrome gelatine compounds proceeded in three principal directions: as a resist for etching, as a mould for electrotyping, and as a printing surface directly. Each of these possibilities presented numerous different ways of applying the principle involved, and it was not long before some of them began to be practised. Immediately after Talbot's publication Paul Pretsch, of Vienna, obtained an English patent for a process of applying the swelled gelatine film as a mould on which to produce electrotypes. By addition of silver iodide to his gelatine solution the swelled films produced a grain of varying fineness, according to the gradation of light and shade of the negatives or positives used for the exposure, thus furnishing photo-reproductions in halftone both in relief and in intaglio.
In the following year, 1855, Pretsch patented a method of producing by this process intaglio-engraved copper cylinders to be used for printing on textile fabrics, a premonition of the rotary photogravure process of the present day.
During these same years Alphonse Louis Poitevin, in Paris, who had previously worked out a method of turning daguerreotypes into intaglio engravings by galvanic etching, was working in the same direction as Pretsch, and in 1855 obtained a patent for a process similar to his. But his really important contribution to the progress of the Techno-graphic Arts was his method of printing direct from the exposed and developed chrome gelatine film on the principle of the lithographic process.
LOUIS JACQUES DAGUERRE, 1787-1851. From a photograph copy of daguerreotype by Charles Meade, Paris, 1848. (Snelling's
Photographic and Fine Art Journal, New York, January, 1855.)
He modified the chrome gelatine solution by adding albumen, gum arabic, and other colloidal substances, and after due exposure and washing out the unreduced bichromate from the film he passed over it a roller carrying a fatty ink which adhered only to those features of the plate that remained dry through having been affected by the light, and was rejected by the moistened ground. From the film thus inked up prints could be taken on paper and, if desired, transferred to lithographic stone and printed from that. So was started at once the practice of photo-lithography and of collotype printing. The former was afterwards, in 1859, simplified and improved by J. W. Osborne, in Melbourne, Australia, through his method of applying the chrome sensitizer to lithographic transfer paper direct, and further developed by numerous other workers of that period. Poitevin's collotype method, that of printing from the gelatine film direct, remained to be perfected by subsequent workers during the decade of the sixties, notably by Jacob Husnik in Prague and Joseph Albert in Munich.
Still another opening was made by Poitevin in the course of his fruitful activity through his application of chrome gelatine films colored with lamp-black or other pigments and dried on paper. By adding other ingredients to the gelatine solution the film became easily soluble in warm water, and was washed away in proportion as it had remained shielded in the exposure. This was the beginning of the pigment or carbon printing process which was afterward improved by John Pouncy in 1858 and practically perfected by J. W. Swan in 1864.
About the same time a new and very important application of the gelatine wash-out principle was made by Walter B. Woodbury through his process of printing with a pigmented glutinous ink. His method was to use the gelatine relief to produce an electrotype from which the glutinous ink, held in the graduated depths of the plate, was transferred to paper in corresponding gradations of quantity, thus producing pictures with a complete gradation of tone. In 1866 he modified the process by replacing the electrotype with a matrix obtained by pressing the dry and hard gelatine relief into sheet lead and transferring the glutinous ink from that. This process, known as the Woodburytype, came into extensive use and held its ground until gradually superseded by the collotype printing method.