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Collodion for Photography

sition, flowing it with the developing solu- Collodion is the vehicle by which the phototion. (See No. 3151.) If properly timed or graphic chemicals are united upon the surface exposed, the image begins to appear. When of the glass and the sensitive coating prethe details of the drapery, if a portrait, ap- duced. It is made by dissolving in equal or pear and the solution seems to have lost its nearly equal proportions of sulphuric ether power, the plate is thoroughly washed under and alcohol, gun cotton or pyroxyline together a stream of clean water. If the image is suf- with certain salts of potassium, cadmium , ficiently strong and vigorous, it is "cleared" by placing the plate in the fixing bath, and that portion of the film not acted upon by the light is dissolved away, leaving the image upon the glass. After a thorough washing in water, the plate is put in a rack to dry, after which it is slightly warmed and varnished. ammonium, &c., in proportions named in the formulæ. Many formulæ are published for this article to which great value is attached, some supposing that to its peculiar composition belong the principal causes of failure or success. This is only in a degree true. Inferior or carelessly prepared chemicals used in any stage of the process impair results. The writer has fixed as a general principle in the