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

[Trevor Cunningham]

  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.
>
> Thanks    Charles   Portland Oregon
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