[Alt-photo] Re: GUM: problematic yellow?

[Marek Matusz]

Luciano,

 

I would say your first set of yellow exposure worked great. Somewhere around 3 minutes looks very good to me. Of course you have to match negative density that spans the steps on your wedge test. You could further alter the look of any layer in development changing time, using spray bottles, etc.

 

The second test with very long exposures revealed just that: grossly overexposed prints and with that also introduction of dichromate stain that shifts the tone of your yellow.

 

For the tricolour gum I mix stock solutions and most of them will separate after days or weeks or months. Just shake well and let the foam subside for a minute or two and they are good to go.

 

Looking forward to see your prints.

 

Marek Matusz
 

> From: luciano at lucianoteghillo.com
> To: alt-photo-process-list at lists.altphotolist.org
> Date: Wed, 5 Feb 2014 18:27:50 +0100
> Subject: [Alt-photo] GUM: problematic yellow?
> 
> After Diana suggestion (thanks again) I was able to source some Fabriano
> Artistico soft-press and I was able to print some exposure tests. The paper
> is great! I am not getting any stains, and finally I am printing something,
> even if they are only step wedges without having to pre-shrink, size, etc.
> etc.... The final test will come as soon as I can print more layers....
> 
> So far no problem with blue
> (http://www.lucianoteghillo.com/images/scan-blue.jpg) and red
> (http://www.lucianoteghillo.com/images/scan-magenta.jpg) but yellow it's not
> printing correctly, at least that's my impression.
> 
> After the first test
> (http://www.lucianoteghillo.com/images/scan-yellow1.jpg) with the usual
> exposure times used for blue and magenta (from 1 minute to 3.30 minutes in
> 30 seconds intervals), it looked like I was not reaching maximum "black" but
> also the steps didn't look as defined as with the other colors. So I decided
> to print one more test with exposures of 16, 32 and 48 minutes
> (http://www.lucianoteghillo.com/images/scan-yellow2.jpg). I think this
> second test is event worst than the first.
> 
> Now everything is the same: same gum, same potassium dichromate, same
> process. I mix a stock solution with 15ml tube and 45ml of gum, which I then
> further dilute as needed. In the case of yellow, I mix 1ml of stock solution
> with 1ml of gum and 2ml of 12% potassium dichromate.
> 
> The watercolor used for yellow is Maimeri Blue, Primary Yellow, PY97
> (Arylide yellow, also known as Monoazo yellow).
> 
> This might be important or not, but I noticed some separation between gum
> and pigment in the stock solution bottle. If I let the bottle rest for a
> day, I can see a ring the color of gum 1/4" thick on top, something I did
> not notice with the other colors.
> 
> Do you have any advice? I do not have other yellow tubes from other
> pigments/brands but I could look for it. It just seems strange that I cannot
> print this color!!!
> 
> Thanks,
> Luciano
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