[Alt-photo] gum 'solarisation' issue

johnbrewerphotography at gmail.com johnbrewerphotography at gmail.com
Sun Jul 30 23:48:33 UTC 2017


Bang on Joe, identical. 

I'll change to another colour that I've used successfully with a one coat when I go to my studio Tuesday. 

Marek, my exposures are typically between 10 and 15 minutes for a one colour one exposure good tonal range print, this for example https://instagram.com/p/BXMI3Q2lMSZ/. No idea on the make of my UV unit, stand uv bulbs, no name Chinese A1 size. 

John

Sent from my iPhone

> On 30 Jul 2017, at 11:32 pm, Joseph Smigiel via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org> wrote:
> 
> John,
> 
> That has happened to me in the past as well. I believe it is staining related to particular pigments. In my case it was Bone Black. I've uploaded a pic showing some tests done with a Stouffer tablet:
> 
> http://smieglitz.tumblr.com/image/163613468740
> 
> Look familiar?
> 
> Joe
> 
> 
>> On Jul 30, 2017, at 1:27 PM, John Brewer via Alt-photo-process-list wrote:
>> 
>> Hi guys
>> 
>> What could cause gum to solarise? It's happening in the light tones, all
>> the dark tones are fine. Stouffer step 1 half on/half off substrate the
>> same. Gradients are fine until step 10 and then it gets darker until step
>> 21. Step 21 visually looks like between step 4 and 5
>> 
>> I'm not doing anything different from the past; gum mixed by me 14 Baume,
>> 13% pot dichromate, M Graham ivory black pigment, FAEW HP 300gsm paper,
>> colorbyte substrate, UV source. As soon as paper is dry it's immediately
>> exposed and then developed. I can't think I'm doing anything different than
>> I have in the past. While I do have a new printer - Epson P600, it's not
>> just that as it's happening on my Stouffer too.
>> 
>> Stumped!
>> 
>> John
>> 
>> -- 
>> John Brewer
>> www.thevictorianphotographer.com
>> www.johnbrewerphotography.com
>> workshops:equipment sales:chemistry sales
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> 
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