If the Pyro "after-bath" is causing an overall brownish stain, it may be
that the developer is exhausted and too oxidized. I suggest your
student use a sodium metaborate after-bath rather than the spent
developer. (Hutchins discusses this in the book.) About 1/2-teaspoon
per liter is the suggested mix, although the exact concentration is not
that critical. The after-bath simply needs to be an alkali solution,
not necessarily the spent developer. If your student is processing his
film in some sort of a rotary system, I highly recommend the Rollo Pyro
version of PMK being marketed by B&S.
Platinum/Palladium Photographs and Workshops
> One of my students has been using PMK for a long time and tells me
> Hutchings likes to put the film back in the developer after fixing to
> increase the stain... Negatives returned to the developer seem
> visually to be more even, but more brown overall. I wonder whether
> increase in stain really evens out the distribution or just makes the
> negative appear more uniform.
> The returning of the film to the developer seems to me to produce a
> general stain across the entire negative and I doubt that it is
> proportional. Seems to me its effect would be with UV processes
> to increase the necessary exposure. With VC silver papers it would
> as an overall low contrast filter. What we would need for UV
> would be the least possible overall staining, but proportional
> can help.