TAIIPENOT'S PROCESS. This is a dry preservative process in which a glass plate is first collodionized and excited, then coated with iodized albumen, and excited a second time. Three years ago, before the problem Of dry collodion was solved, this process, disco vered by Dr. Taupenot, Professor of Chemistry at a French college, was brought forward and excited so much attention that it has not even yet been completely abandoned by amateur photographers for the better process of Dr. Hill Norris, of Birmingham, since disco vered and perfected.
The operations are as follow :— A plate is first collodionized and excited in the usual way. It is then washed with distilled water for the purpose of removing the free nitrate of silver. A mixture containing about equal parts of albumen and water, and 1 per cent. of iodide of potassium, is then poured over it. This completely destroys the sensitiveness of the plate, which may then be dried in daylight before a fire. It is now ready to be excited a second time. This is effected by immersing it in a bath of aceto-nitrate of silver, containing 50 grains of nitrate of silver and 1 dram of acetic acid. The plate is then washed with distilled water, and either dried by artificial heat, or allowed to dry spontaneously. It is now ready to be exposed in the camera, and
may be kept for several days, or perhaps weeks, in a sensitive state.
The picture is developed by first steeping the plate in a dish of distilled water for a minute or two, then laying it upon a, levelling stand, and pouring over it a saturated solution of gallic acid to which a few drops of aceto-nitrate of silver are added. It is fixed in the usual way with hyposulphite of soda, not cyankle of polanium ; for the latter salt should never be used with albumen films, as it acts too energetically upon albumen.
The pictures obtained by this process have a yellowish or greenish tint, and are not therefore suited for transparencies.
The collodion should be porous and adhesive, and not hard and contractile, or blisters will be produced when the film is wetted a second time.
The objections to the process are,—the multiplicity of operations,— the bad colour of the pictures,—and the discoloration of the second nitrate bath. As a set off to these objections it has no advantage whatever over dry collodion.
The plates may be developed more quickly with pyrogallo-nitrate of silver, but the definition is not quite so good, and stains more liable to occur.