Alkaline Stopbath

Although it is more convenient to use an acid stop bath and fix, simply because they are more readily available, it is far better to keep the whole processing procedure at or near the ph of the developer, and developers are alkaline! Up to now there was little choice; you took your film from an alkaline developer and plunged it into an acid stop, followed by an acid fixer. These radical changes in ph stress the emulsion, and can play havoc with those delicate (and not so delicate) highlights you worked so hard for.
Now there is Alkali-STOP, the world’s first, and as far as we are aware, the only alkaline stop bath. Available only from Monochrome Photography, and designed to work with Prescysol (and other staining developers) and Alkali-FIX, our own alkali fixer.
It is known that an acid environment inhibits the formation of the stain so desirable and effective in producing fine negatives, but keeping the ph within certain tolerances not only enhances the stain, but has other benefits too.
Alkali-Stop is the worlds first genuine, commercially-available alkaline stop bath. It works quickly and readily and produces clean, white highlights and well-balanced mid-tones. (Surprisingly, an acid stop, if over-used, can give a slight stain in highlight areas, and slightly muddy mid-tones that do not clear in the fix.)
No matter which film or developer you use (even when lith printing) using an alkali stop bath and fix will mean shorter washing times, meaning a saving on time and water. You do not need a hypo clearing bath for prints, and the toning qualities of prints will be enhanced too.
Alkali-STOP is supplied in a 500 ml bottle as a concentrated stock solution. The stock solution is diluted 1:9 to make a working solution.

Alkali-STOP is fast-acting. Immerse films and papers for up to 10 seconds only, agitating continuously, drain and transfer to the fixing bath. The working solution can be stored and re-used, and each litre will process at least 60 films or 25 8x10 prints. Total capacity is
therefore approximately 300 films or 125 prints. Discard the used stop if it discolours to yellow.

An effective test to determine if the Stop is still active:
In the darkroom, take a small, unexposed piece of paper and develop for your normal time. Drain, and submerge in the Stop, agitating, for 30 seconds.
Remove the test strip and turn on the room lights; if fully stopped the paper will remain white, or show a slight yellow stain (which disappears in the fix) depending on the kind of paper. If the paper is not stopped completely it will continue to develop, eventually turning black.