> I used this process about 12 months ago using saturated potassium bichromate &
> gum based glue. It worked though not very consistantly. Unfotunately I did not
What is "gum-based glue"? Gum Arabic? You mixed from powder or bought
lithographer's gum? What's the preservative? Gum can go bad; bad gum
won't clear.("Glue" means something else in UK than in US?)
Are you using the same paper? Same brand paint? Same colors? Certain of
these can totally fog gum -- or not clear.
I take it you're using remains of the same dichromate solution, but my
tests show that ammonium dichromate does age in a year. It will print,
but gains speed -- "same" exposure could be too much.
Heat and humidity can also cook gum, though if you expose as soon as
print is dry it'll be OK.(I print all thru NYC unairconditioned summer.)
Are you drying the coated paper with heat? That's always a no-no, but
combined with warmer weather & older sensitiser could be last straw.
Are you waiting longer to expose? In hot weather that's also risky.
And incidentally, Luis, I coat gum by ordinary room light (about 10 feet
from north-facing windows), or you can't see what the hay you're
doing -- or I can't. I've even left paper to dry in the light (this is a
test!) and got passable image. Naturally, for best results, one dries
in the dark. I use electric fan, no heat. One
set of tests showed best print on paper about 2 hours old,
though that probably varies with the paper and everything else. Anyway,
drying method is a BIG variable.
Judy
PS. Anthony, hope you'll let us know when you solve the problem(s) what it
(they) was (were).
PPS. Heat of direct summer sun can also cook gum. "Open shade" is safer.