Quote Originally Posted by Claire Senft
Bob one technique that I have used to increase film speed that does not increase contrast is to prebathe the film prior to development in a solution of 1% sodium perborate.

This should give a doubling of speed with any black&white film with the contrast and grain size staying the same.

Claire,

I was intrigued by this suggestion, since I'd not heard of it before, despite some 35 years in the film-developing game. Maybe I did, but it didn't register on the radar. Anyway, I tried it today. Took my Rollei SL-66 out with two backs, each loaded with Delta 400. I have previously established that for my developer, ISO 200 is normal. So I shot one roll at 200 and the other at 400 (to be treated with the perborate solution later). I metered for a Zone V exposure, (high, bright, even overcast) and then shot several bracketed exposures of each scene with each back.

I treated the roll shot at 400 in the perborate and then developed both rolls at my usual time in my usual soup (Phenidone, Vitamin C, metaborate). I then contacted and made prints from several of the scenes from both rolls. Strangely, I did not get the increase in film speed you suggest--at most about a third of a stop. In fact, in each case, the roll shot at my usual 200 and left untreated by the perborate was the better negative, giving me the fullest range of tonal values and shadow detail without blocking highlights.

Is it possible, do you think, that the T-grain structure of Delta film is not susceptible to this pre-development treatment? Perhaps I should try again using FP4+ or Fuji Neopan which are more conventional grain films?

I did not notice any increase in grain, as you said would be the case. It's a simple treatment, but only worth it if it really does increase film speed.

Larry