SPUR Ultrafix N is a slightly acid fixer concentrate (around pH 6), 1 litre, for film and paper.
What it is for
The everyday working fixer. Its mild acidity is the compromise: enough to neutralise carried-over developer, but not as aggressive as a classic hardening acid fixer, and far less trouble at the washing stage.
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
Cheaper and more universal than the alkaline Ultrafix A. Take the alkaline one only if you develop in staining developers or print a lot on baryta.
