Hi bob
No a consensus has not been reached yet in regard to the most effective
method of removing Dichromate stain [ or in fact what Dichromate stain is
] , but I expect that all the methods will work in the right
circumstance. As the Chinese say many paths lead to heaven not just one. I
am in the middle of testing at the moment and hope to report back to the
list next week with some observations.
Now to deal with your particular problem, first of all Bob it would help to
know which paper you were using. I have been using the1% sulphuric acid
with my students Kingsway College KTC for a number of years, and found
that on 95% of the papers used this works fine but on the other 5% we
experienced the same problem that you describe, this is one of the great
things about teaching you acquire a lot of information from your students.
When this first happened I considered what action to take. The acid content
could be increased, sulphuric acid is a nasty substance so I ruled this
out on health and safety grounds, also there could be archival
considerations.I think the problem maybe caused by the paper containing to
much alkali, which neutralised the acid before it could start working on
the stain.so what I did was to give the the offending print a soak in
5%sol of meta bisulphite first this changed the stain to blue/green/grey
then transferred the pint to the 1% sulphuric acid and this seemed to do
the trick.
If you do try out Terry's long soak technique if you could inform me of the
results I would be most interested as I intend to include all this
dichromate stain information in my next book
hope this helps pete