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

Katharine,

Thank you for taking the time to look at my webpage and read it.

You are absolutely right that the labeling is backwards on the 7 and 15% am
di image. I had decided to change it from left to right and forgot to
change the text. It is, as we speak, redone and sent to my trusty web
designer.

As far as not seeing the stain issue, I apologize that it isn't visually
clearer...the letters of the weakest exposure are basically the same color
as the pigment stain, but it may be that I should take that image off the
web because it isn't clear enough, or redo it to show it more clearly.

Thanks for the input,
Chris

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@usask.ca>
Sent: Thursday, July 13, 2006 3:11 AM
Subject: Re: Determining SPT with gum Was: Gums a la Demachy and Puyo

>
> On Jul 12, 2006, at 7:34 AM, Christina Z. Anderson wrote:
>
>>
>> BTW, to all: How do you determine your standard printing time with gum?
>>
>> Loris,
>> If you go to:
>> http://www.czaphotography.com/show.php?what=learning&which=1
>>
>> on my website and scroll down a tad, you will see images related to this
>> question
>>
>> David is totally right in that gum is not like the others in choosing
>> SPT, because if you think about it, when exposing, let's say, pt/pd, you
>> look for max black in Step 1, but the paper absorbs the chemistry, it
>> doesn't get thicker like gum does. So what I did was quite arbitrary,
>> and was to choose a time that allowed complete development in 1 hour
>> just letting the print sit there, but also produced a nice punchy
>> colored layer. The layer is stable, does not whoosh off, and allows
>> spray development if I want to shorten the development time to 1/2 hour
>> (spraying after a 5 or 10 minute soak). Once I chose this arbitrary
>> time (UVBL 6mn, under 15 watt bulbs) then I printed my 101 step palette
>> and derived my curve from this.
>
>
> Chris, what you're saying here, as well as the images themselves, seems
> to support what gum experts have been recommending for decades, to
> determine the exposure time for gum not by some complicated process but
> simply to use a step tablet to establish the time required to give the
> deepest tone possible for that particular emulsion, as well as a stable
> gum layer.
>
> A criticism re the presentation of the images: some of the text
> accompanying the images is contradicted by the visual evidence. Your
> caption says, "Too little exposure is weak and has a tendency to stain
> more readily because there is no hardened gum to trap the pigment and
> keep it from sinking into the paper fibers." However, in the step
> tablets above the caption, of the five tablets representing five
> different exposures, the only one showing significant pigment stain is
> the one on the far right, the one with the most exposure. And the
> letters below the caption, exposed at different times, show no
> difference between the exposures that I can see as far as stain. I keep
> hearing this assertion, that stain is inversely related to exposure,
> but my own tests don't support it, (see my page on stain for test images)
> and I have yet to see data from anyone supporting this assertion.
>
> Also, the blue circles a bit farther down that purport to show that more
> dichromate doesn't give more hardening: could those perhaps be
> mislabeled? It would make more sense if the tablets on the left
> represented 7% and the ones on the right 15%, but it's labeled the other
> way around.
>
> Sorry, but part of my job for years was writing, editing and critiqueing
> scientific articles, so things like this jump out at me.
>
> Katharine
>
>
>
>
>
>
>
Received on 07/13/06-10:30:40 AM Z