Moersch Citric Acid Stop Bath is a citric acid stop bath, 500 ml concentrate, for film and paper.
What it is for
Citric acid instead of acetic is above all about smell: in a small darkroom the difference is immediate. The maker is honest, though, and promises no complete absence of fumes: any acid meeting an alkaline sulphite developer produces some, and paper developers carry a lot of sulphite. Only replacing the stop bath with a water rinse removes it entirely.
How to dilute it
The solution is replenishable — kept and reused, with development time extended as it exhausts. Keep count of the films put through it; that is the only way to avoid an underdeveloped roll at the end of its life.
Storage
Sealed concentrate keeps well but dislikes air: the emptier the bottle, the faster it oxidises. Decant the remainder into a smaller bottle, or displace the air — that is what gets a concentrate to its last measure.
How it compares
The catalogue already carries ADOX Adostop Eco with an indicator. An indicator is convenient because exhaustion shows as a colour change; this stop bath is simpler and cheaper.
