Re: Tonal inversion (was (Gum) Tonal scale)

Yves, et. al.,

I just realized this effect is probably also related to specific
pigments. (This would also support what Tom has observed IIRC, and
perhaps also to Chris' observation regarding pH.) The reversal effect
appeared when using bone black as the pigment but not cobalt violet.
Each was given the same exposure which presumably would lead to similar
heating of the test wedge (assuming the integrator is working correctly
on the exposure unit). Since the bone black reversed and the cobalt
violet didn't, something else must be contributing to or causing the
effect.

You are correct in that it may be very difficult to isolate the exact
cause of the effect without introducing some other variable. I
certainly don't have the means to do so.

Still, it appears I have overexposed the bone black test by roughly
3.5-4 stops so I'll run a test at a much shorter and more normal
exposure to see if the reversal effect dissappears at that level.

Joe

---
>>> gauvreau-yves@sympatico.ca 12/03/05 12:10 PM >>>
Joe,
This may well be the way to check this idea out but as you say it may
introduce something else in the process. I think it would be somewhat
complicated to verify this, with a high degree of certainty in practice.
In my own test, this happened to me as well and as soon as I reduce
exposure
a bit it didn't happen. This makes me believe that there could be
somekind
of threshold involved but again this is all very speculative on my part.
Maybe someday I'll have the time and the money to investigate crazy idea
like this one.
Thanks
Yves
----- Original Message -----
From: "Joe Smigiel" <jsmigiel@kvcc.edu>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, December 03, 2005 11:44 AM
Subject: Re: Tonal inversion (was (Gum) Tonal scale)
> >>> gauvreau-yves@sympatico.ca 12/03/05 11:06 AM >>>
> >>... I think it could be caused by heat...<<
>
> I agree.  This seems to be plausible explanation for the effect.  I'll
> run a couple more tests reducing exposures or perhaps doing
intermittent
> ones to keep the negative (test wedge) from overheating and see if
that
> has any impact (although I might be introducing some sort of weird
> intermittency effect by doing so).
>
> Joe