Re: (Gum) Tonal scale

Clay,

I like this, I couldn't find the words to say it as well as you did below
but it is exactly my opinion that there is no way a physical particule
doesn't play at minimum a physical role in this gum "reaction".

Thanks
Yves

----- Original Message -----
From: "Clay" <wcharmon@wt.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, December 01, 2005 9:44 AM
Subject: Re: (Gum) Tonal scale

> I've been following this thread on an off for the last few days.
> While I agree with you that the photochemical reaction taking place
> is ONLY influencing the physical property of the gum itself through
> crosslinking, is it not also true that the pigment itself influences
> the wavelength of the light actually absorbed by the gum layer below
> the surface. IOW, is not a yellow transparent pigment naturally
> going to filter the light to some degree and pass more lower
> frequency light to the gum than would a layer pigmented with say, a
> transparent violet color? My sense is that pigment, while not
> involved in the hardening reaction of the dichromated colloid per se,
> is indirectly involved in the manner that it allows UV radiation to
> be absorbed in the coated layer of gum/dichromate/pigment. Thoughts?
>
>
> Clay
> On Dec 1, 2005, at 7:58 AM, Katharine Thayer wrote:
>
> >
> > On Nov 30, 2005, at 9:46 PM, Judy Seigel wrote:
> >
> >>
> >> I didn't understand much of the discussion about printing clear
> >> gum arabic, partly because I didn't understand it, partly because
> >> I didn't think I needed to understand it, and partly from
> >> suffering from turkey poisoning. But I think one point needs to be
> >> made -- or repeated: Results with plain gum arabic and dichromate
> >> without pigment will NOT replicate results *with* the pigment. Or
> >> let me correct that to say, I doubt that they would or could.
> >
> > Hi Judy,
> > Of course; and I think I've made that point several times, but
> > perhaps not clearly enough, in discussing all the different ways
> > that pigment can affect the tonal scale. My point about the
> > unpigmented gum was to emphasize that while the pigment does
> > provide the tonal scale, it does not participate in the reactions
> > which constitute the response to exposure, so unlike silver
> > printing and many other photographic processes, with gum you cannot
> > draw a curve relating exposure to *density of reaction product* to
> > tonal scale. Hope that's clear as unpigmented gum,
> >
> > Katharine
> >
Received on Thu Dec 1 09:44:11 2005