[alt-photo] Re: no shrink, no size tricolor gums

[Loris Medici]

Hi to both of you, joining just to make few comments: (I hope I'm not
misunderstanding you both...)

- Do not take it as a dogmatic(*) rule or something, but: I think most will
agree on the principle that it's "good and just"(!!!, See note * -
hehehe...) to follow a parameter set that will keep "still development"
times around 30 minutes...
- Assuming you're giving good exposure (criteria: layers will fully develop
in 30 minutes, w/o dichromate stain, flaking or loosing highlights...), with
gum, dmax isn't dependant on exposure but pigment color and load... More
exposure won't increase dmax; you have a limit, which is dictated by the
pigment(s) you've put into your coating solution.

Good luck,
Loris.


-----Original Message-----
From: alt-photo-process-list-bounces at lists.altphotolist.org On Behalf Of
Trevor Cunningham
Sent: Tuesday, September 14, 2010 11:36 AM
To: The alternative photographic processes mailing list
Subject: [alt-photo] Re: no shrink, no size tricolor gums

  Hey Charles, I'm in a similar pickle. I can imagine shrinkage has a lot to
do with climate. Here in the Arabian desert, I'm also going through some
tri-color gum trials too. I did a preshrink and am very glad I did. My first
attempts were using rabbit skin glue as a size. Now I've moved to cyanotype
as the first layer, followed by an unhardened gelatin size and the
subsequent layers. I had whittled my exposure down to one minute in the
blazing sun, but fear this is too little as I've lost dmax and/or the
emulsion just slides right off in patches. And, actually, I'm losing
emulsion in the border areas where it should be getting nice and  toasty
burnt. I wonder is:

   1. Should I be a little more aggressive and try to brush off the
      residue and live with the dmax and recoat that color?
   2. Should I increase the exposure? I've exposed another print at two
      minutes, so we'll see how that goes, or should I expect more of
      the same?
   3. I'm mixing my gum 1 part gum to 6 parts water and the AD is
      roughly 1:3. I use these solutions at 1:1. I wonder if increasing
      my dichromate might also do the trick?


On 9/12/10 11:08 PM, Charles Ryberg wrote:
> I'm trying to make tricolor gums on FAB using the no shrink, no size 
> method mentioned here recently.  I have made three curves which appear 
> to give good results as far as color and tone go, but they require at 
> least an hour wash per coat.  I'm having registration problems which I 
> think might be caused by the excessive soaking--so, I want to try new 
> color mixes (and, of course, calculate new curves) which will clear 
> more quickly.  My current mixes are made from (pigment/gum/water 
> stock), gum, saturated potassium dichromate all three in equal
> volumes.       I expose for between 4 and 6 minutes (depending on 
> color) under BL tubes.
>
> My guess would be to expose less and accept some loss of DMAX.  Could 
> I make up for this by increasing the pigment load?
>
> Any other suggestions.  Please remember the goal is not to size.