STEEL ENGRAVING. The comparative softness of copper occasions copper plates to wear so rapidly in the process of printing, that the beauty of the engraving is very soon ims. paired, and it is impossible to produce from a single plate, a sufficient number of impres sions for the illustration of books of large circulation. The use of steel plates for dimin ishing this inconvenience, although not exten sively resorted to until within the last thirty years, is a measure of which the possibility was conceived at an early period, but which was first put into practice about thirty years ago, in the attempts to protect the Bank of England notes from forgery.
In Messrs. Perkins and Heath's method of steel engraving (which has been the basis of all recent modes of producing large numbers of copies), the engraving is executed upon a plate or block of cast steel, the surface of which has been decarbonised or softened by a careful application of heat. On the plate thus softened the engraving is effected with facility ; and, when it is completed, the hard ness of the surface is restored by exposing the plate for some hours to a red heat, the surface being thickly covered with animal charcoal, formed of burnt leather or bones, and the whole being, as before, enclosed in a cast iron box. The plate is afterwards cooled and retempered in a very 'careful manner. From this hardened plate the engraving is transferred to a softened steel roller, of small diameter, which is pressed against the plate with such force that its surface becomes em bossed with a perfect transfer or impression of the engraved device. The roller or cylinder is then hardened in a similar manner to the original plate, and is afterwards made to transfer the devices from its surface to any required number of softened or decarbonised plates, which are then hardened for printing from. This beautiful process is not only ap plicable to transferring engravings from one plate to another ; but, in cases where pne ornament has to be repeated several times on one plate, the device may, by being once en graved, be impressed as often as necessary upon different parts of the same plate. The
power of multiplication is, for all practical purposes, unlimited. It is by such a process that the postage stamps are produced, millions of impressions being obtained from only one originally engraved plate. The perfection which has been reached is almost beyond con ception ; the finest writing, and the most minute and intricate patterns, being trans ferred from plate to plate with such precision that the keenest scrutiny cannot detect a dif ference between the original and the transfer. The plan has been much used for country bank-notes and similar purposes.
The application of steel engraving to works of fine art is, in a great measure, due to the late Mr. Charles Warren. In this method, the steel is softened to receive the graver, and is printed from in this softened state. The surface of a steel plate is not polished very highly, and in applying etching ground to. it, the plate is not heated quite so much as is usual with copper. In the application of steel engraving to matters of fine art,, the ae• complishment of mersotinting upon steel plates is one of the most important points, as the wear of copper plates engraved in this manner is very rapid.
The cyst of engraving upon steel is consi derably greater than that of engraving upon copper ; yet, as steel plates afford so many more impressions than copper, they enable the publisher, by calculating his returns upon a large instead of a small number, to issue works of art at so low a price as to ensure a very wide circulation.