The Dictionary Of Photography

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

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Restrainer
In the finished print about ...        ... 3 per cent.
,, cuttings about ... ...        ... 7 ,,
,, washing, before toning, about   50 to 55 ,,
.. fixing bath.........        25 .. 30 ..
,, washing after fixing ...        ... 5 n
Restrainer. Any substance used to prevent the too energetic reducing or developing action of any chemical upon the exposed film. Restrainers may be of two kinds - mechanical and chemi-cal. To the first class belongs water or any tanning agent, as chrome alum, which renders the gelatine less permeable to the developer. To the second class belong any soluble bromide or chloride, and the citrates of potash, soda, and ammonium. A soluble bromide is added to the developer to check the reduction of the unaltered silver bromide, the soluble bromide seemingly forming a double bromide with it, which is less acted upon by the developer. The restraining power of the bromides of ammo-nium, potassium, and sodium bear the following proportion to one another: - Bromide of ammonium - 98 parts are equal to 119 parts of bromide of potassium, and equal to 103 parts of bromide of sodium. Bromide of ammonium is, therefore, the strongest, potassium bromide the weakest, and the sodium salt the medium. The citrates of potassium, sodium, and ammonium seem to act in entirely a different manner; whereas the bromides prevent the excessive deposit on the high-lights to some extent and allow detail to appear, the citrates prevent detail and allow density to be obtained. To make these restrainers, the bromides can be simply dissolved in water, as follows : -
Ammonium bromide ... ... ... 98 grs.
Distilled water, to make......... 980 mins.
of solution, each drachm of which will contain 6 grs. of bromide.
Potassium bromide          ... ... ... 119 grs.
Distilled water, to make ... ... ... 980 mins.
of solution, each drachm of which will containgrs. of bromide of potassium, equal in restraining power to 6 grs. of bromide of ammonium.
Sodium bromide ... ......... 103 grs.
Distilled water, to make ... ... ... 980 mins.
of solution, each drachm of which will containgrs. of sodium
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