Page:The New International Encyclopædia 1st ed. v. 16.djvu/470

PRINTING. to fine engravings in relief. Crude experiments at soldering composed types together and at making duplicates by the pressure of pages on type metal softened by heat were made in the eighteenth century, but the first practical work was done by William Ged, a goldsmith, of Edinburgh, in 1725. His invention was not kindly received by the printers and publishers of England, and soon fell into disuse, but it was revived and improved by Earl Stanhope of London, about the year 1802. For nearly fifty years afterwards it was preferred for book work, and was generally known as the plaster process. The page of type to be stereotyped was put in an iron pan and a preparation of plaster of Paris poured over it, which was afterwards baked dry in an oven. The dried mold so made was then submerged in melted type metal that penetrated every crevice. When properly cooled, the mold was broken, and a duplicate of the composed type appeared on one side of the plate. The rough side of the plate was planed down, its edges were beveled, and faulty letters corrected, until it became a presentable duplicate of the type work. Stereotyping by plaster was brought to Newark by David Bruce in 1813. Stereotypes have also been made by pressing the types upon prepared dampened china clay, but the clay process is rarely used. The papier-maché process, invented by Genoux, of France, in 1820, was neglected for many years, but is now in favor with all daily newspapers. Sheets of thin tissue paper, pasted together and backed with damp unsized thicker paper, constitute the mold or matrix for the papier-maché process. They are firmly and evenly impressed on the page of type, which may be flat or curved, and are then dried upon the page. When dry the matrix is removed, and adjusted to an iron mold on which melted type metal is poured from several openings. The plate so made is then cooled, planed, and beveled to fit the press. All the operations, aided by machinery, are made with great speed. Ten minutes is the ordinary time.

For fine book work and for duplicating engraved illustrations, electrotyping is the process preferred. By this process the type page is impressed in a thin sheet of wax which is first dusted with a coating of powdered graphite and then with a coating of iron filings. The wax mold so prepared is immersed in a bath containing a solution of sulphate of copper through which passes an electric current from a dynamo. This deposits a thin film of copper on the wax mold. (See .) When thick enough to be stable the film or shell of copper is backed with a solder of tin, and afterwards with a firmer basis of type metal, applied in a melted state. This type metal base is then planed and beveled, so that it can be neatly fitted to a thicker base of hard wood that makes it type-high. Electrotype plates may be curved by passing them through shapers or suitable bending rolls. Electrotype plates for printing were made by Joseph A. Adams, a wood engraver of New York City, in 1839-41, but they did not supplement stereotype before 1850.

Printing ink is a trituration (not a chemical union) of boiled oil, smoke black, coloring matter, and other ingredients. By the old process for inking types, stuffed leather balls were made use of, but they were difficult to keep in proper order, and were inapplicable to

cylinder printing. The first improvement on the stuffed balls consisted in covering them with the elastic composition of glue and treacle then employed in the Staffordshire potteries. Catching at this idea, the inventors of cylinder printing machines made inking rollers by casting them in a cylindrical mold. This invention came generally into use between 1814 and 1818, everywhere superseding balls, and rendering printing machinery practicable. Inking rollers for type work, now made of a mixture of glue, glucose, sugar, and glycerin, are found more durable than those made from glue and molasses only. The quantities of each constituent must be varied to suit the speed of the machine, the nature of the presswork, and the temperature of the press-room.

The earliest engraving of a printing press shows a stout framework of wood posts, firmly braced against the ceiling to resist upward pressure, a bed plate of stone as a rest for the form of type, which could be exposed to receive ink, and then be slid upon ways under the platen or pressing surface. Impression was given by a large screw of wood over this platen and this screw was moved by a long bar of wood and iron. The sheet of paper to be printed (about 16×20 inches was a common size) was laid upon an inclined framework of wood covered with blanket or parchment, which was hinged to slide on the ways and to be placed under the platen. This platen impressed only one-half of one side of the paper; to print the sheet 16×20 on both sides the pressman had to give four pulls on the bar. To print with uniform margin and in accurate register, the sheet on its first impression was pierced with small perforations on the front side, and afterwards suspended from holes so made on properly placed points when the second side was printed. Although the mechanism of the press was rude and even petty, good printing was done upon it by a competent pressman. The first improvement in construction was made by Blaew, of Amsterdam, in 1601, who in addition to other devices attached springs to the platen moved by the screw, so that it could have a quick return movement without special exertion from the pressman. In 1786 M. Pierres, of Paris, invented a printing press entirely of iron, and strong enough to print one side of the sheet by one pull of the bar, but it did not meet with favor. About 1804, Earl Stanhope, of