Page:The American Cyclopædia (1879) Volume X.djvu/535

LITHOGEAPHY 529 Edwards, and others, in their collographic pro- cesses, which are of so much importance at the present day. Joseph Dixon, late of Jersey City, published the essential features of this process in 1854; but his experiments were of a somewhat incomplete nature, and not sufficient to displace the claims of Poitevin. Messrs. Out- ting and Bradford of Boston, Mass., patented a photo-lithographic process in March, 1858. They sensitized the stone much as Poitevin did, using bichromate of potash, gum arabic, and a little sugar. They exposed it however under a transparent positive, and washing the stone with a solution of soap, succeeded in ma- king those parts of it take the ink which were unacted on by light; the altered gum pro- tecting the other places from the soap water. In this case the lithographic work was actual- ly on or in the stone. A suitable etching re- moved the altered gum after rolling up. M. Asser of Amsterdam was the first to suggest a transfer process. This invention was made early in 1859, but not published till November. His method consisted in sensitizing a sheet of unsized paper, or one slightly sized with starch, with bichromate of potash ; exposing the same under a negative ; washing the resulting print with water; drying and heating it strongly upon a hot plate ; and finally again moistening and rolling up with transfer ink. The trans- fer sheet so prepared gave an inky positive pic- ture, corresponding with greater or less fideli- ty to the lights and shades of the negative. After completion it was transferred to stone, which was then etched in the usual manner and printed. This process, like all the prece- ding, never gave results of commercial value. J. W. Osborne, then of Melbourne, Australia, in August, 1859, invented the photo-lithographic process which bears his name. He prepares a sheet of paper by coating one side with a viscid solution, consisting of a mixture of al- bumen, gelatine, and bichromate of potash; this, after being dried in the dark, is exposed under a negative of the original to be repro- duced. The photographic positive picture thus obtained is inked all over while dry by pulling it through the press face down, in contact with a lithographic stone to which an even coating of transfer ink has been applied. When the sheet is removed from the stone, the adhe- sive ink covers its surface, and nearly conceals the underlying photographic picture below it. This sheet is next placed floating on hot water, with the inked side upward ; the moisture and heat together effect a coagulation of the albu- men in the compound organic film, while the gelatine portion of the same gelatinizes and swells. The sheet is now lifted from the water, laid flat upon a slab, and friction ap- plied to its inked surface by means of a wet sponge. The superfluous ink not needed to form the transferable picture is hereby re- moved; the sheet is flooded with abundance of warm water, dried, damped again slightly, and transferred to stone by simply inverting it thereon and pulling it through the press in the usual way. When removed the ink on the surface of the transfer sheet will be found to have passed over to the stone, which is then rolled up and etched, after which it is ready for the printer. In this process the albumen plays an important part ; its insolubility after coagu- lation prevents the undermining of the finer details by the solvent action of the water, and it also sticks the sheet to the surface of the stone during the operation of transferring, thereby preventing any shift and consequent doubling of the work. This process is chiefly adapted for copying line engravings, drawings, manuscripts, &c. ; and this is also true of all analogous methods. It was adopted by the government of Victoria in September, 1859, for copying and publishing maps and plans; and since that time many thousand originals have been reproduced, being at present almost the only means employed there. This pho- to-lithographic process was the first which proved of real practical value. In 1865 the American photo-lithographic company of New York was organized, and has since worked this process with unvarying success. The drawings of the patent office for several years, and those of other governmental bureaus, have been executed by its means, whereby a great saving in cost and innumerable advantages in promptness and accuracy have been secured. In August, 1861, Mr. Hannaford of London suggested a photo-lithographic method, which he never reduced to practice, but which M. Toovey of Brussels subsequently patented. Al- though this process has not come into general use, it must be regarded as essentially typical in its nature. Mr. Hannaford recommended the preparation of a sheet of paper with bichromate of potash and gum, its exposure under a nega- tive, and its transfer while damp, without ink- ing, to the stone. The consequence would be the passing over to the latter of more or less gum from the unexposed and unaltered parts, where- by the stone on such places would be incapaci- tated for receiving ink. If we now attempt to roll up the transferred surface with ink, we shall find the latter to adhere only to the clean parts of the stone, forming there the litho- graphic picture. In addition to the six essen- tially different processes which have been de- scribed, there are numerous others based upon them, which it is unnecessary to particularize here. As early as 1841 the late Mr. Joseph Dixon of Jersey City, and Mr. Lewis, a li- thographer of Dublin, Ireland, each made at- tempts at the production of pictures on stone from which impressions could be printed. Mr. Dixon used bichromate and gum, much as Poi- tevin did. Mr. Lewis prepared a card surface with hard transparent ink, gave the same a thin coating of metallic silver, and then, pro- ceeding as in the daguerreotype process, man- aged to expose certain portions of the under- lying ink, which he then transferred to stone. The experiments of both these gentlemen were