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

Re: Tricolour gum and PDN

Hi Henry,
Separate the positive into RGB channels. Convert the RGB negs back into RGB because they are greyscale now. Then invert, and then put your curve adjustment layer on top of each separate negative, and the PDN color layer on top of that. I don't know if this is what you are already doing but it may help if not.

BTW, according to Sam Wang diluting cyanotype sensitizer makes it a bit slower and more contrasty but not lighter. I actually mix my cyanotype at 2A:1B, even. Be sure you are printing the cyano layer with the R neg, too?

One interesting thing I notice--gum over cyanotype, being that it is acidic, tends to make the cyanotype nice and blue. You will notice that where the gum does not cover the cyano it washes to a paler blue gray, but underneath the gum it is good and dark.

It is a PITA when the cyano goes too dark on you, isn't it--you can't scrape it off.

I'm sure this goes without saying that the cyanotype curve is different than the gum curves?

When you figure it out I hope you post your results to the list.

----- Original Message ----- From: "Henry Rattle" <henry.rattle@ntlworld.com>
To: "alt photo process" <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, September 02, 2006 2:35 PM
Subject: Tricolour gum and PDN

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!