Re: Back-exposing on plastic (was: Re: Gum transfer

Katharine,

ok so it would seem we have the same notion that contrast means a difference
between to things, in the context of photography this would mean the
difference between tones, color, densities, etc.

Sandy King wrote many things about the carbon process and one of them is
this in the context of carbon printing and relief, when coating tickness is
relatively high, he suggest to lower the percentage of pigment, lower the
percentage of dichro (to barely a trace, almost) and for this to work
exposure time will have to be increase quasi exponentially. The relief
obtain using this method should be in the high range and this make sence,
with optimise values for each dependent variables, light as more chance to
go deeper into the emultion thus resulting in a higher relief. With a thin
coating, more pigment and dichro are required and exposure as to be much
shorter then for tick coating.

A minimalist interpretation of all this would suggest that contrast (which
is somewhat related to relief) is dependent on the combinaison of all
dependent variables (tickness, % pigment, pigment, % dichro, exposure time,
etc) and not just on the % dichro or any other variable taken individually.

If we apply (and can apply) the same reasoning to back exposed gum, then it
may very well be possible to decrease the percentage of dichro by a
significant factor say 5x or more, optimise the other variables for this
level of dichro and obtain useful results. I understand gum and gelatin are
not the same material but I would think they are close cousin sort of speak
and sure the actual numbers and characteristics will be different but not to
the point where we can't see some familarity between the two, in other
words, the "contrast" between the two should be relatively low.

It is with those ideas in mind that I didn't understand your "Well, for me
5% gives too much contrast already, so I sure wouldn't want anything less".
Early on, if you recall, I express my concern about the huge space one would
need to explore in order to have a wide angle view or understanding of the
gum process. Back then, I used different words but essentially I figured out
early on that with all the variables in play in the gum printing, not to
speak of the interrelations between them, all this strongly suggested to the
technical buff that I am, the underlying space of possibilities is just
huge, this would take anyone a very large chunk of time to be spent learning
this space emprically. The almost childish recommendations I received then
was to put on glove, take some gum , some pigment, some dichro, some paper
and go make some prints, all this while trying to have fun. Anyway, this was
a "long" time ago and this kind of thread kinds of confirm my original
concern about the huge possibilities of the gum process.

Regards
Yves

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@usask.ca>
Sent: Tuesday, May 02, 2006 1:04 PM
Subject: Re: Back-exposing on plastic (was: Re: Gum transfer

>
> On May 2, 2006, at 9:16 AM, Yves Gauvreau wrote:
> >
> > I'm sure this is a misunderstanding (on my part) or a different
> > interpretation of what "contrast" means and since you have much more
> > experience on this then I do, would you be so kind to explain
> > further what
> > you mean. "> Well, for me 5% gives too much contrast already, so I
> > sure
> > wouldn't
> > want anything less."
>
> Too much contrast, in the context of the print I was talking about,
> means that the tonal gaps between the printed tones are too great,
> giving sharp, jerky transitions between tones. In the face, for
> instance, there are only two tones, and there's a sharp edge between
> them, which is what I meant when I said the tones in the face are
> posterized.
> kt
>
>
Received on 05/02/06-12:48:34 PM Z