Etching, Engraving and the Other Methods of Printing Pictures by Hans Wolfgang Singer William Strang

Author:Hans Wolfgang Singer , William Strang
Language: eng
Format: epub
Publisher: K. Paul, Trench, Trübner & Co., ltd.
Published: 1897-03-25T05:00:00+00:00

CHAPTER XII

THE PLANOGRAPHIC PROCESS. LITHOGRAPHY

|HE art of lithography depends upon the chemical antagonism existing between fat and water upon a surface that possesses like affinity for both.

As the name indicates, this surface was originally (and is to this day in the majority of cases) stone. Suitable kinds of stone have been found in various parts of the old and new world. By far the best, however, is brought from Solnhofen, in Bavaria. This stone is a form of calcium carbonate or carbonate of lime. It is cut into slabs of different sizes, each from two to three inches in thickness.

The lithographic draughtsman draws his design upon such a stone with an ink that contains tallow, wax, soap, shellac, and fine Paris black. When the drawing is finished a very weak solution of acid is poured over the stone. This ' etching * of the stone is generally done by the lithographic printer, and very often he spoils the work. For it is a difficult affair, and requires an accurate knowledge of the strength of the acid, which when slightly too strong will wash away the more delicate portions of the drawing. The solution decomposes the carbonate of lime in the stone as well as the soap in the ink ; the lime and fatty acid thus set free combine to

122 THE PLANOGRAPHIC PROCESS, LITHOGRAPHY

form an insoluble soap. Furthermore, the solution of acid renders those parts of the stone which have not been drawn upon still more averse to accepting any fatty substances, and their resistance is increased by the addition of a solution of gum arabic. Before an inking takes place the printer moistens the stone every time with a sponge, so as to make sure that the gummed portions will perform their functions, for if the stone gets dry anywhere it will be ready to receive the fatty ink from the roller at that place.

If such a stone be inked with a roller, only those parts that have been drawn upon will accept the lithographic ink, while those that have been treated with acid, gum, and water repel it Thus a method has been found to print from a block without resorting to the practice of either relief-cutting or intagliating.

The lithographic press consists of a running plate, covered by a thick sheet of felt: upon this the stone is placed face upwards, and the sheet of paper, with some extra * backing' to soften the pressure, on top of this. Then the scraper is lowered from above to the stone. The scraper is a three-cornered piece of wood extending across the breadth of the press, with one of the corners protected by a strip of leather pointing downward. It is so adjusted that it can be moved up or down according as the stone is thick or thin. It is set fast along one end of the stone so as to exercise a pressure upon it The stone is now run along under it, whereby the paper is scraped down against the inked surface, thus causing an impression.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.