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

[Loris Medici]

Luciano try to evaluate the yellow test prints by splitting RGB channels
and looking to the B channel. Since it's a very light color it's hard to
judge it by eye...

Regards,
Loris.


2014-02-05 Luciano Teghillo <luciano at lucianoteghillo.com>:

> ​...
> 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.
> ​...
>