Submitted by Al …
(Adapted from The Encyclopedia of Photography ©1963)
In order to control the alkalinity (pH) of a developer, buffering is often resorted to. With developers of the metol-hydroquinone-borax type, such as Eastman Kodak’s D-76, an increase in alkaline content is apt to result after mixing, and this increase causes increased development speed and increased graininess. Boric acid and borax are often used as a buffer to help remedy this increase.
A typical buffered borax solution is the following solution:
Metol 2.0 grams
Hydroquinone 5.0 grams
Sodium sulfite 100.0 grams
Borax, granular 8.0 grams
Boric Acid, crystals 8.0 grams
Water to make 1.0 litre
Actually, most developers are buffered to some degree, as many of the salts are buffering agents. Unlike replenisher, which keeps the developer up to general strength, the buffer keeps the developer at correct working strength but does this by keeping some alkalinity in reserve and releasing it as the alkali in solution is used up. Thus, the buffer is a sort of regulator which maintains constant alkalinity in a solution, while at the same time only a small amount of alkali is ever available at any time.
In the buffered developer recipe given, the amounts of boric acid and borax are equal. For greater of less activity, the proportions between the two can be varied – more borax speeds up the developer, while more boric acid slows it down. This method of slowing down a developer is preferable to merely reducing the amount of alkali. If the latter is done, the developer will quickly become exhausted, since there is no more alkali available when that in the solution is used up.
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