The ferrotype plate is a sheet of iron covered with an insoluble black varnish and coated first with a bromo-iodised collodion. Pour a pool in the centre, flow round the edges, and pour off at the bottom right-hand corner. When the film has set, which is shown by its dulness, it is laid face up on a dipper - two pieces of glass cemented together - and lowered into the silver bath consisting of silver nitrate 31 gr., distilled water 1 oz., and 1 drop of a 10 per cent, solution of nitric acid and distilled water. After one minute's immersion it is withdrawn, and, if wetted evenly, requires only two minutes longer. Drain and wipe the back with blotting paper, and place in the dark slide. Slides for the wet process have wires on which the plates rest, and a gutter at the bottom for drippings. Exposure is as usual, but wet plates are considerably Less sensitive than dry plates. Great care must be exercised to keep the films free from dust. For development the plate is held in the hand and flooded with sulphate of iron 5 gr., acetic acid 5 c.c., alcohol .5c.c, water 80 c.c. Fix in cyanide of potassinm 2gr., water 30 c.c.

To intensify or brighten, reduce the deposit on the shadow portions, and allow the dark plate to show through more. Drops of 10 per cent, solution of iodine added to the fixing bath have the desired effect. Ferrotype cameras are fitted with a number of lenses and divisions in the camera. A repeating back - that is, a frame with a hole over which the slide passes so as to expose a portion of the plate at a time - may be used with a spring catch in the top slide rail to register positions.