The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Diazotype or Primuline Process
by pressing with glass rods, etc., and stirring about. The material, after about five minutes' immersion, should be allowed to drain, rinsed once in cold water, and dried. In this stage it is not sensitive to light, and the dipping and drying may be effected in daylight. It will also keep well in this condition. The drying should be rather rapid, and therefore blotting off between blotting paper, or a free current of air, should be resorted to. The sen-sitising solution is composed of
Sodium nitrite         ... ... ... ... 4 parts.
Oxalic acid ...         ... ... ... ... 6 ,,
Distilled water         ... ... ... ...1,000 ,,
In this the material should be immersed and well saturated, then drained, rinsed, and superflous moisture removed by pressing be-tween thick blotting paper. The material need not be absolutely dry, and should be exposed at once, as it will not keep. The sensitising and drying must be done in a dark room or by weak gaslight. As this process is whdt is called a negative printing process - that is, it yields a negative from a negative - we require a positive to obtain a positive. The material is then exposed under a positive for kabout thirty seconds in sunlight, to ten minutes or more in diffused light. The process of printing can be gauged to some extent by examining the material in the ordinary way, the action of light bleaching the material, which assumes a dingy colour. It is advisable till practice is secured to use small test pieces of material, exposing them side by side with the printing frame till they no longer give colour with the developer. The developers are as follows : -
For Red Tones.
/3-napthol ... ... ... ...        ... 6 parts.
Sodium hydrate ... ... ...        ... 8 ,, .
Distilled water         ... ... ...        ... 1,000 ..
For Yellow Tones. Carbolic acid (crystal) ... ... ... 10 parts.
Distilled water         ... ...... ... 1,000 ..
For Orange Tones. Resorcin ... ... ... ... ... 6 parts.
Sodium hydrate ... ... ... ... 9 ,,
Distilled water         ... ... ... ...1,000 ,,
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