Re: Tricolour gum and PDN

["Christina Z. Anderson" <zphoto@montana.net>]

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.
Chris


----- 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!
>
> Best
>
> Henry