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

[Loris Medici]

Thanks John, that's what I do because I'm incredibly incompetent in judging
the yellow test prints. I just can't make sense of those yellow step tablet
prints with naked eyes. (Blue rich light helps, though...)

Did the trick on Luciano's print and I think 3:30 or even 05:00 will give a
nice log 1.2 - 1.3 range, but that depends on his target DR. I don't think
something over 05:00 will do good.

Regards,
Loris.



2014-02-05 John Brewer <johnbrewerphotography at gmail.com>:

> That's a useful tip Loris!
>
> J
>
> Sent from my iPhone
>
> > On 5 Feb 2014, at 09:12 pm, Loris Medici <mail at loris.medici.name> wrote:
> >
> > 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.
> >> ​...
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