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

[Trevor Cunningham]

  I'm struggling with the yellow layer right now. You know, "flaking" is 
the perfect word for what's happening to me. I soak for about 1/2 hour 
and while it seems the dichromate clears, the gum/pigment stays. So, 
soaking for more time, and a little spray/brushing leads to the 
unsightly flaking. I got so fed up I just started scrubbing yellow off 
the print. Using DaVinci Aureolin. If the answer is in the curve (I'm 
using David Hatton's gum curve from the altphoto site), I don't even 
know where to begin. I saw a note from Christine saying most gum trouble 
comes from coating too heavy...I wonder if that's what I'm doing wrong.

On 9/14/10 11:55 AM, Loris Medici wrote:
> 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.
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