Take a developing tray larger than the negative to be stripped, pour in sufficient water to cover, and, for a whole plate, drop in 8-10 drops hydrofluoric acid (the exact quantity cannot be given, as the strength of the acid is constantly diminishing, though kept in a guttapercha bottle); place the negative in the acidulated water, and in a minute or two the film will frill all round the edges and gradually leave the glass. If the operation is slow, add 2-3 drops more of acid, and gently rock.

When the film is loose, hold it at one end, pour off the acid water, and wash by repeated changes of water; this lengthens the film wonderfully, but if the last washing is done with equal parts of methylated spirits and water, it will return to its original size. This may be varied considerably by using more or less spirit. But on no account should undiluted spirit be used, as it makes the film coil out of all control.

Clean a plate with nitric acid - larger than the stripped film - dust with French chalk, polish with a dry cloth, and with a wet one wipe 1/4 in. all round, coat with plain collodion, and when set, or even quite dry, introduce under the film. Adjust the film, and with a little:

(a) Pyrogallicacid .. .. 2 gr. Citric acid...... 3 gr. Water .. .. .. 1 oz.

(b) Silver nitrate .. .. 20 gr. Citric acid...... 60 gr. Water .. .. .. 1 oz.

Commence the development with (a), and add a few drops of (6) now and then as required. With a properly exposed plate, the development will be gradual and entirely under control. If the solution becomes turbid or discoloured, it must be changed at once. Any deposit that forms on the surface of the plate may be removed by gently rubbing with a tuft of cotton-wool. If full density is attained before the detail is all out, either the exposure has been too short, or too much silver has been added during development. If, on the other hand, when the detail is fully out, the density is insufficient, too little silver has been used. If, however, the development is skilfully managed and the plate properly exposed, full detail and density will be obtained together.