Photogravure

About the year 1820 Nicéphore Niepce made the discovery that bitumen, under certain conditions, was sensitive to light. He dissolved it in oil of lavender, and spread a thin layer of the solution thus obtained upon stone. This he exposed under a drawing (making the paper transparent by waxing), and after sufficient exposure, oil of lavender was poured on. Those portions of the bitumen which had been exposed to the action of the light had become insoluble, and so remained while the lines which had been protected by the drawing were dissolved away. By treating the stone with an acid these lines were bitten or eroded, and could be printed from. Niepce afterward employed metal plates instead of the stone. For many years, however, progress in processes for intaglio printing was very slow. In 1852 Talbot introduced a process termed photoglyphy, and in 1854 Paul Pretsch, of Vienna, patented a process which he termed photogalvanography. In 1870 the late Walter B. Woodbury, inventor of the Woodburytype process, suggested to M. Rousselon, of M. M. Goupil & Co.,[A] a process which he had discovered, and which he describes[B] as follows: "The method, as perhaps many of your readers know, is based on the fact that some pigments used in carbon printing have an unpleasant habit of granulating when mixed with gelatine and bichromate, destructive to their use in carbon printing and Woodburytype, but bearing the essence of success in an engraving process where grain is necessary. The origin of this method was simply owing to my getting some bad reliefs, in which this effect was first noticed. Out of this arose the photo-engraving process which, as I said before, is now claimed as the invention of a Frenchman. But I am digressing. "This relief, possessing a suitable grain, could, by hydraulic pressure, be made to transfer its minutest details to metal without any loss to fineness, so giving a plate possessing all the properties of a mezzotint. The methods hitherto used of electrotyping would have proved useless, as all detail would have been lost. The same thing applies to the new method I am now about to bring before your readers. The latter process of getting the grain transferred to a hard metal remains the same; but the novelty is in the method of producing the grained plate. To those who have practiced the process of enameling, as used by Geymet and Alker, and others, my description will be better understood

Dettagli