A change every 10 minutes.
Actually I would use shorter times for early baths and increase the
time for later baths, since the idea is to reach equilibrium (equal
concentration of chemicals in the paper, emulsion and water) at each
step. I sometime leave images soaking overnight for the last step,
expeccially when its late and I'm tired.
You also don't need a mass spectrometer to predict what the final
residue of fixer (or whatever you are trying to wash out) could be is.
rec.photo.darkroom has the calculations in some posts in the last
couple of years (dejanews might find them). Briefly its the ratio
of the volume of the piece of paper to the volume of the wash, raised
to the power of the number of baths (an 8x10" sheet one mm thick is
1x20x30/1000 = 0.6cc washed in one litre for 6 baths gives
( 6x10e-4) ** 6 = 4.6e-20 which is not much!
Sandor Mathe -- sandor.mathe@prior.ca
(905) 670-1225 x333
FAX (905) 670-1344