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 07/13/06-03:10:48 AM Z
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