If the film is processed correctly, there should be no silver remaining.
The ferric ammonium EDTA converts the silver to positive ions ("cations"),
Na++. The ammonium thiosulfate fixer converts the Na++ to a variety of
silver thiosulfate complexes, which get washed out in water.
If the film is properly fixed, all the silver will be gone.
The principle is the same for RA4 paper. RA4 blix is ferric ammonium EDTA
and ammonium thiosulfate. C41 "blix" is also based around ferric ammonium
EDTA and ammonium thiosulfate. The reason that many C41 kits use separate
C41 "bleach" and "fix" steps is that using a ferricyanide bleach is cheaper
than the ferric ammonium EDTA (but they are chemically antagonistic). It
doesn't cost the kit mfgr anthing more to do the extra 6 minute step!
(There is a slight difference in Fujiflex RA4 paper, which uses a platinum
catalyst; though all the silver is removed blix, not all of the Pt metal is
removed. Someone who does chemistry professionally should be answering this
question, not me!)
- Don Feinberg
ducque@xxxxxxxxxxxxxx
>
> Can someone more knowledgeable than me please confirm that in
> traditional colour processing - negative C41 and print RA4
> processes, that the end result, negative or film, will not
> contain any *silver* grains at all?
> My understanding is that the bleach fix step if properly
> applied converts all silver metal to silver cations (by the
> ferric containing EDTA, and the ammonium thiosulfate then
> removes all the silver halide, i.e. silver cations?
>
> A colleague on another forum has suggested that all colour
> prints produced by the wet colour print process will show
> silver grains...
> He quoted the Kodak reference:
> <http://www.kodak.com/global/en/professional/support/techPubs/
> e58/e58.jhtml
> <http://www.kodak.com/global/en/professional/support/techPubs/
> e58/e58.jhtml>>
> as confirming his point, but it doesn't tie in with the
> chemistry that I understand. I think they are using the
> silver grain produced in traditional B&W prints as the
> standard for comparison.
> (I'm probably being very pedantic here!)
>
> Howard
>
