[Alt-photo] gum 'solarisation' issue

johnbrewerphotography at gmail.com johnbrewerphotography at gmail.com
Sun Jul 30 21:54:26 UTC 2017


Thank you Marek for your comments. I'll certainly try the flash exposure. My exposures are around 15 minutes. What would you recommend as a base starting exposure at my printing exposure time? 

I didn't think about paper, it is a new batch since last time I printed (Fabriano EW HP 300gsm) and I read manufacturers 'improve' their paper to the detriment of alt printer regularly here!

John

Sent from my iPhone

> On 30 Jul 2017, at 10:05 pm, Marek Matusz via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org> wrote:
> 
> John
> 
> 
> Here is my observation. I have seen it with some pigment more then others. Likely to be related to the old "stain wars". To me this is the way gum layer interacts with paper. Totally unexposed gum is so "porous" it lets some of the pigment bind with paper as it fissolves. You need a little bit of gum hardening (just ever so slightly, to where it is still soluble) to hold the pigment together where it can be washed away without biding to paper.
> 
> A short pre-exposure without negative helps as it introduces this slight amount of gum pre-hardening. I also find that it extends tonal range. This is also more likely to be happening on the first layer of gum in the multilayer process and with some sizes more then others as some sizes will attract pigment more then others.
> 
> Also as I noticed it will happen more with some pigments then others.
> 
> 
> Why all of the sudden? Could be as simple your paper changed. Same brand, but manufacturers tweak papers all the time. Additional sizing should help.
> 
> Let us know what happens.
> 
> 
> Marek
> 
> 
> ________________________________
> From: Alt-photo-process-list <alt-photo-process-list-bounces at lists.altphotolist.org> on behalf of John Brewer via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org>
> Sent: Sunday, July 30, 2017 5:27 PM
> To: The alternative photographic processes mailing list
> Subject: [Alt-photo] gum 'solarisation' issue
> 
> 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
> 
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