In this process all the above operations may be performed in ordinary white light. To render the plate sensitive, heat it as hot as the hand will bear, and when cool immerse it again in the following aceto-nitrate of silver bath for one minute, using only a yellow light, then wash thoroughly in clean water and dry in the dark:
Nitrate of silver
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The development may he commenced by either plain or alkaline pyro; Mr. Mudd gives the preference to the plain, and intensifying after with acid silver.
Dr. Ryley's Modified Collodio-Albumen Dry Process. In this method the plate has to be sensitized as usual and washed thoroughly. When the plate has been well drained, and while still wet, it is coated with the following solution:
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The solution is beaten to a froth, allowed to settle, and filtered before using. Pour sufficient over the plate to cover it, letting it flow backwards and forwards so as to soak into the film. Pour the albuminous solution away and thoroughly wash the plate, the last rinsing being with distilled water. Let the plate dry; when perfectly dry moisten the plate with distilled water and pour over it the following solution:
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Pour it on and off the plate to well permeate the film, then set the plate up to drain, and dry without washing off the gallic acid solution. When the surface is dry finish by the heat of a dull fire.
To every ounce of good collodion add 8 grs. of bromide of cadmium. The nitrate bath must be made 80 grs. to the oz., and slightly acidulated with nitric acid. The plate must remain in the bath the full time it requires to form a dense opaque film. When the plate is ready (it must not be removed from the bath until the film is much denser than in the ordinary wet process) it must be washed thoroughly to remove all silver. It must then have poured over it a 3 grs. solution of gelatin made slightly alkaline with carbonate of soda, or diluted albumen (albumen 1 oz., water 4 oz, well beaten together). When the plate is in this condition it may be exposed wet, or it may be allowed to dry. . Prior to development it must be well washed, and the alkaline method must always be adopted. If the plates are used dry, a preliminary coating of dilute albumen is necessary, but if used wet, this is not necessary.
By this method the nitrate bath is not necessary as the sensitive material is contained in the collodion. The purchase of the material ready made for working this process is recommended in preference to its direct manufacture, as its preparation demands the use of considerable technical skill, together with the employment of a gun cotton not usually attainable. Mr. Hughes says the " Liverpool Dry Plate Company " supply an excellent emulsion. It is only necessary to pour the emulsion on to a plate and to allow it to dry, when the plate is ready for use. The development is by the alkaline process.