U of S | Mailing List Archive | alt-photo-process-l | Re: Tricolour gum and PDN

Re: Tricolour gum and PDN

Yes, I made the same observation some time ago.

PDN will allow you to calibrate your workflow in such a way that you will get an almost 'perfect' negative for many processes, meaning that the range of the negative is calibrated to the range of the process.

But gum has a rather short range of densities anyway, and even a 'perfect' negative for gum is only the starting point for making a print. You will probably have to expose several times, probably also each time with a different mixture composition and exposition time.

This for monochrome work. Color is no different and even more complex. In my experience, at least, separation negatives made with the help of PDN cannot just be superposed on a print as if they were monochrome negatives. You will get a print which is too dark.

What I do is cut exposition time, but I admit that this is a rather empirical procedure that makes PDN little justice. Probably more calibration is necessary, based on the finished color print.

Tom Sobota

Henry Rattle wrote:
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!