RE: Determining SPT with gum Was: Gums a la Demachy and Puyo

Yep. Additionally as Katharine pointed out (and kindly tested), results with
mixtures may not come out as you expected. As for making the color muddy:
Don's right, but I think that will occur only if you add too much black - my
suggestion was to add very little black. Anyway, you have many options to
try now - please return us with the way works for you later.

BTW, to all: How do you determine your standard printing time with gum?

Since calibrating Argyrotype I determine SPT by overexposing a step tablet,
then scan it, average the tone in the steps, change the mode of the file to
Lab, create a new grayscale file from the Luminance channel and use the
levels adjustment tool with the Alt key to locate the first black square.
Then I make the necessary exposure time adjustment (by counting steps below
the first black and reducing the exposure according to this) and retest
(using the same step tablet along with the CDRP) to see if everything's
right and to determine the negative color. It was surprising to see that the
density I was choosing with the former method (visual inspection of the step
tablet) was often 1-2 steps off (overexposure - I was often choosing an
exposure time which causes solarisation = less dmax)... What would be your
comments on this?

Regards,
Loris.

-----Original Message-----
From: davidhatton@totalise.co.uk [mailto:davidhatton@totalise.co.uk]
Sent: 12 Temmuz 2006 Çarşamba 11:27
To: alt-photo-process-l@usask.ca
Subject: RE: Gums a la Demachy and Puyo

Hi Loris,

I understand what you're saying - a different curve..

David H

On Mon, 10 Jul 2006 16:33 , Loris Medici <mail@loris.medici.name> sent:

>Maybe you can add a little ivory black (a very warm black) to your
>Vienna Red. But keep in mind that the mixture may behave quite
>differently than the single color.
>
>Regards,
>Loris.
>
>-----Original Message-----
>From: davidhatton@totalise.co.uk [davidhatton@totalise.co.uk]
>Sent: 10 Temmuz 2006 Pazartesi 12:44
>To: alt-photo-process-l@usask.ca
>Subject: Re: Gums a la Demachy and Puyo
>
>Hi All,
>
>While we patiently wait for Terry to finish his garden..What other
>pigments would Demachy use for one coat gums? Plus, how do I modify
>Vienna Red to be darker? Is it possible? I've looked on the internet
>and the pigment (red Oxide(?))in some images seems to have a darker tone to
it than mine.
>
>David H.
>

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Received on 07/12/06-03:58:58 AM Z