Re: Gum hardening: top down experiment

Marek,

maybe this will save you time and effort, if your front exposed print didn't
hold any pigmented gum on the substrate doesn't this prove to you that the
hardening happen from the surface down, otherwise even the lightest exposure
relatively speaking should start hardenning your gum immedialy at the
surface of the substrate and a minimal amount of pigmented gum would be
expected to stick on the substrate especially if it does when exposed from
the back.

Just a thought, regards
Yves

----- Original Message -----
From: "Marek Matusz" <marekmatusz@hotmail.com>
To: <alt-photo-process-l@usask.ca>
Sent: Tuesday, April 11, 2006 10:41 AM
Subject: RE: Gum hardening: top down experiment

> Katharine,
> I was very impressed with your results and thanks for contributing to this
> discussion in a positive and constructive way. Looking at your scans I
would
> conclude that heavily pigmented gum layers on unabsorbant substrate do
> harden from the top down, just like other dichromated colloids. I see very
> nice tonal gradations in the print exposed from the bottom. The three
> variables (gum, dichromate and pigment ratios) are not optimised, but at
> this point I am looking for illustration of principles, rather then
perfect
> prints.
> I did a similar experiment last night. I coated a heavily pigmented and
> thick layer of gum on a transparency material that I use to print
> diginegatives (HP brand). This brand has a nice sandy feel to it, so I
> though it would help to hold the gum. I exposed coated pieces for twice
my
> usual times, one through top, the other from the bottom. The piece exposed
> from the top flaked off rather quickly leaving no image. The was no image
> that I could see at any point. The piece exposed thorough the bottom once
in
> the water started behaving like a carbon print, where the colloid was
> dissolving in water, rather then flaking off. After about 3 minutes I was
> excited to see a full tonality image, with beautiful tonal gradations.
> Unfortunately the image continued to develop even afet I took it out of
> water and hanged it to dry. This morning there was only a faint image left
> on the piece of transparency. I will give it another try with much longer
> exposure and perhaps lower dichromate to get more depth of UV penetration
> and hardening and higher Dmax.
> Marek, Houston
>
>
> >From: Katharine Thayer <kthayer@pacifier.com>
> >Reply-To: alt-photo-process-l@usask.ca
> >To: alt photo <alt-photo-process-l@sask.usask.ca>
> >Subject: Gum hardening: top down?
> >Date: Mon, 10 Apr 2006 11:33:03 -0700
> >
> >Okay, I've coated a very thick, very heavily-pigmented gum emulsion on
> >mylar and printed it from the front and from the back. A couple of
> >comments before I give you the URL:
> >
> >(1) though the emulsion was very heavily pigmented, two things resulted
in
> >not a very deep DMax: (a) the fact that I used ivory black, a
transparent
> >pigment (if I were to do it again, I'd use lamp black) and (b) the
fact
> >that it's printed on a transparent material and was scanned as a
> >transparency, with the light shining through it. But the thing to note
is,
> >be that as it may, the DMax is about the same in both prints.
> >
> >(2) there's a light brown pigment stain (ivory black is a brownish
black)
> >in both prints that is probably a function of the heavy pigmentation. It
> >hardly shows in the prints themselves, but for some reason was
> >accentuated in the scanning.
> >
> >(3) I don't honestly know what to make of the results. If you look just
at
> >the prints on mylar, you'd have to conclude that back- printing is much
> >superior to front-printing, at least for a thick coat on mylar. But if
you
> >compare the back-printed print on mylar to the regular front-printed gum
> >print (using a less heavily-pigmented emulsion) on paper (at the bottom
of
> >the page), it's hard to claim that the back-printed print is superior.
But
> >since they are on different materials, it's apples and oranges.
> >
> >So I guess if I were forced to draw a conclusion from this rather
> >inconclusive test, I'd say that if you are going to print on mylar
using
> >a very thick and heavily pigmented emulsion, then you'll probably do
> >better printing from the back. But if you're printing on paper, you can
> >get fine results printing from the front with a less pigmented emulsion.
> >
> >http://www.pacifier.com/~kthayer/html/topdown.html
> >
> >Katharine
> >
>
Received on Tue Apr 11 09:03:40 2006