"David Littlewood" wrote in message
...
In article , Gregory L. Hansen
writes

The local one-hour photo labs have very little ability to do special
requests like pushing film. And surely for good reason. But what would
happen if they just ran it through the developer machine twice? As I
recall, at some point it goes through a fixer bath that, well, fixes it,
and maybe it can't be developer further at all after that. But my
knowledge of the chemistry is really pretty sketchy.


As others have told you, once it has gone through the fixer all the
undeveloped silver salts are removed, and that's it. However, if the
film was put through the developer twice without having been fixed in
between, then development would continue and you would get a grossly
over-developed film. Assuming it is negative film, the highlights would
be completely blocked up and the contrast would go through the roof; the
results would almost certainly be unusable. It is possible to gain some
extra film "speed" by using a shorter exposure and a longer development
time, but this would usually only be about 20-30%, and the film has of
course been underexposed to compensate (though you still get increased
contrast). It is however difficult to do this in a mechanised C-41
process line, as the timings are usually fixed. Also, they usually put
the film through all the baths (including fixer) with no chance to get
it out in mid-process.

David

I worked with a lab that could push process by simply shutting off the
machine while the film was in the soup, before the stop and fix stages.
Unfortunately, they could only do it with 24 exposure rolls, as a whole 36
exp. roll was never all in the soup at one time.

--
Regards,
Matt Clara
www.mattclara.com