In an earlier post I described my frustrations at getting air bubbles on my negatives as a result of poor agitation technique. But I was wrong …
Investigating this, I decided to look more carefully at my agitation technique. Firstly, I placed a spiral into a tank and filled the tank with water to the appropriate level, just above the depth of the spiral. I then agitated in my usual way for a minute, inverting the tank continuously and slowly. After the minute, I rapped the tank smartly onto the bench and then opened the tank.
Air bubbles clustered in the spiral just below the water level. So rapping the tank did not remove the air bubbles. I had always assumed that it would remove them.
So next I thought that perhaps each agitation cycle simply replaces a cluster of air bubbles with new ones, albeit in a different place. I figured that as long as you kept agitating frequently, then each set of air bubbles did not stay on the film edge for long enough to cause problems in the development of the negatives. My air bubbles were caused by failing to completely invert the tank thereby not displacing each set of air bubbles on each agitation cycle.
So I tried out a new test film with HC110 developer, but this time completely inverting the tank on each minute and rapping the tank smartly against the bench. The result is the photograph above. Problem not solved!
I trawled through the internet for possible solutions. None found. By chance at the time I was re-reading a small book published in 1965 called ‘Photographic Chemistry’.
On page 73, in a section called ‘Rinse baths’, I read the following:
‘With some emulsion-developer combinations, plain running water is adequate (for a stop bath), but in many cases an acid is added to make the bath more effective … The stop-bath prevents brownish-coloured stains sometimes formed by the action of the oxygen in the air on the alkaline developer on the surface of the film’.
This would seem to explain the problem I have had. I have been using plain water stop baths because I have been using non-hardening alkaline fixers. When I returned to using an acid stop bath, the staining stopped.
So it seems that the problem was not one of air-bells due to poor agitation, but staining due to an improper stop bath process for the film film/developer combination that I was using. Actually, if you look carefully at the top edge of the photograph, it is obvious that it is staining! Duh!