When I still did single transfer, I used sodium bisulfate. However I
noticed that the yellow stain is transferred to a brighter grey/greenish
"fog", esp. after using a higher (3-5%) concentration of dichromate as
sensitizer and with thick transfer papers. It just became visible at the
edges where the tissue was. I got rid of this by "painting" the transfer
paper with sensitizer while the sandwich was waiting for development. So
it became grey everywhere...
Now I develop on plexi or white plastic and then transfer to paper and
see no need for clearing.
The hardening I do with 3-5% glyoxal. G. is said to be much safer than
formalin. Our (missed!) Judy I think first suggested it for sizing
papers for gum printing and it works fine for carbon, too.
Klaus Pollmeier