BACKING-UP.
The thin copper-plate, when removed from the wax mould, is just as minutely correct in the lines and points as was the wax mould, and the original page of type. But it is obvious that the copper sheet is no use to get a print from. You must have something as solid as the type itself before it can be reproduced on paper. So a basis of metal is affixed to the copper film, and this again is backed up with wood thick enough to make the whole type-high. To get this, a man melts some tinfoil in a shallow iron tray, which he places on the surface of molten lead, kept to that heat in square tanks over ordinary fires. The tinfoil sticks to the back of the copper, and on the back of this is poured melted type-metal, until a solid plate has been formed, the surface of which is the copper facsimile and the body white metal. The electro metal plate, copper colored and bright on its surface, has now to go to the