Slow plates giving extreme contrasts such as are used for photomechanical work are the only ones suitable for use in photo-copying pencil drawings. Many workers prefer to use the wet collodion process for such work, as this, with intensification, gives extreme density and contrast. When the drawings are faintly done upon a blue tinted paper, it is practically impossible to obtain sufficient contrast, and the only plan is to make a tracing in a good black ink or ebony stain. This may then be easily photographed or copied the same size by exposing beneath it a sheet of ferro-prussiate paper.