Tricolour gum and PDN

[Henry Rattle <henry.rattle@ntlworld.com>]

I wonder if anyone who has used PDN for tricolour gum can help?

I've made a number of tricolour gums in the past (some examples on the
alternativephotography site - thank you Malin) but was encouraged to try the
PDN system by Christina's convincing comparisons between tricolours made
with standard and PDN negatives. (incidentally, I echo the appreciative
comments for Christina's books - best read since Post-Factory!)

The PDN process worked perfectly - a cyanotype print with every step of the
21-step clearly distinguished, and a full range of tones in the print.
Similar outcomes for one-coat gum.

However when I set out to make tricolour (or CMYK) gum over cyanotype, I run
into problems. After separating the channels, all three (or four - I've
tried both RGB and CMYK) negatives seem very thin and flat, so that using
the full standard printing time I end up with colour layers that are way too
dark. Even diluting the cyanotype solution 1+4 still ends up much too dark.
Yet I note from Christine's workflow that she uses more or less full
strength classic cyanotype solutions. Am I missing something obvious?

Any shared experience would be most welcome!

Best

Henry