When only a small edition of a book is wanted the printing is generally done direct from the types, but when a large number of copies is required or frequent editions are expected, stereotype or electrotype plates are made. By this means the types are released for further use and other advantages obtained. Stereotype plates are cakes of white metal carrying merely the face of the types, and were formerly made by taking from the types a mould of plaster of Paris. They are now formed by beating or pressing a prepared pulp of papier-mâché into the face of the lettering. The mould thus obtained is dried and hardened by heat, then molten metal is run into it of requisite thickness. This plate after being properly dressed is fitted on a block equal in height to the type stem, and takes the place in the frame or chase that would have been occupied by the types. The process of stereotyping is fairly quick and economical, but electrotypes are better suited for higher class work and are much more durable. In this process an impression is taken from the type on a surface of wax heated to the necessary degree of plasticity. When the wax mould has cooled and hardened it is placed in a galvanic current, where a thin coat of copper is deposited on its face. This coat is then detached from the mould and backed with white metal to give it the requisite body and stiffness and the electrotype is now, like the stereotype, a metal plate which can be fixed on a block and secured in a frame ready for the printing machine. It is outside the scope of this work to describe minutely the marvellous machinery used in printing. It is interesting to know that the first printers had no machine but a screw handpress by which they laboriously worked off their books page by page, and that even so late as the middle of the nineteenth century all books with scarcely an exception were printed at handpresses which enabled two men to throw off about two hundred and fifty copies of a comparatively small-sized sheet in the hour. Now the machines commonly in use, attended by only a man and a lad, throw off from a thousand to fifteen hundred copies in an hour of a sheet four or even eight times the old size.