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

Katharine,

bellow you say "675 g dry ammonium dichromate in 5 ml" and it seems you
might have mean milligrams (mg) instead of grams (g).

Back exposing seem to make a gum emultion behave like a carbon tissue where
percentage of dichro as low as 1/2 % have been used. I wouldn't be surprise
to ear you can make a relief gum print with back exposure. I suppose it is
just a question of finding the right ratio of tickness and finding the
proper concentration and quantity of each ingredient to use.

This not a critic of Marek, you or anyone else but I don't know, I can see
the benefit of using some plastic and back exposure for somekind of
transparent presentation which could be somewhat magical but I don't see how
one can present such a piece without taking advantage of its transparent
nature. It would be like trying to show a large Velvia slide (4x5 or more)
laying flat on a piece of white paper if you see what I mean. Makes me
wonder if we should continue to call these "print", maybe calling then
"slides" would be more appropriate, just a thought.

Regards
Yves

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@usask.ca>
Sent: Monday, May 01, 2006 8:28 PM
Subject: Re: Back-exposing on plastic (was: Re: Gum transfer

>
> On Apr 27, 2006, at 9:14 AM, Katharine Thayer wrote:
>
> >
> > On Apr 26, 2006, at 2:56 PM, Marek Matusz wrote:
> >
> >
> >
> >> The total volume of the solution is incidental as it only serves
> >> to dissolve everything and make the solution spreadable. Once the
> >> gum dries, it is the weight of dry components that will determine
> >> final properties of the mixture.
> >>
> >
> > Seems plausible in theory, but given my own observations over time
> > I wonder if this is so. I might have to drop my cleaning and
> > sorting and try mixing a different dichromate solution to see if
> > less dichromate in the same amount of water has the same effect. If
> > so, then I'd have to agree that the reduced DMax in #3 is caused by
> > something other than more water in the emulsion.
>
> Marek, I'm glad you're still working at this. This afternoon I took
> the time to do this experiment, to satisfy my own curiosity re your
> assertion that it's the weight of dry components, rather than the dry
> components as a proportion of the total volume, that determines the
> properties of the emulsion. I found, at least in this experiment,
> that neither of us was exactly right; the answer fell somewhere in
> between.
>
> To review: last, I showed a back-exposed print made with 2.5 ml of
> 33% paint/gum mix and .5 ml of saturated dichromate, in other words .
> 135 g dry dichromate in 3 ml total volume coating. I found this mix
> to be too contrasty. Then I showed a print made with 2.5 ml of the
> same paint/gum mix and 2.5 ml of saturated ammonium dichromate, or .
> 675 g dry ammonium dichromate in 5 ml of total emulsion. I found this
> mix to give insufficient DMax, which I attributed to the extra water
> in the coating, and to be a bit too low in contrast.
>
> Today I mixed some ammonium dichromate at 1/5 saturated, to give
> (theoretically) the same dry weight, .135 g ammonium dichromate, in 5
> ml total coating. In other words, this tests whether I was right in
> attributing the reduced DMax in last week's print to the extra
> water. This print came out between the earlier two prints (neither
> too contrasty nor not contrasty enough) with DMax also between the
> other two. It could have benefited by a slightly longer
> development, but it's just a test print, after all, and it's
> obviously on the right track as far as the tonality. But weirdly,
> there's a graininess to it that isn't in the other two prints, which
> I can't explain. It doesn't show well in the jpeg, but the right hand
> and the face are very granular in quality.
>
> For further explorations, I need a better negative (this one I'm
> using wasn't particularly intended to produce a long tonal scale) and
> will continue along this line of thinking: about 33% paint/mix,
> about 5% ammonium dichromate. It's interesting that I need much more
> pigment and much less dichromate when back-exposing on
> transparencies, to get the same kind of print I get with less
> pigment and more dichromate, front-exposing on paper. I don't quite
> see why that would be, but it seems to be, nonetheless. I added this
> print to the page I showed last week, for comparison.
>
> http://www.pacifier.com/~kthayer/html/topdown4.html
>
> One more caveat: I exposed all of these for 2 minutes in the sun,
> but of course differences in the UV intensity at different times
> could be responsible for some of the differences.
>
> Oh, and by the way, I got some new inkjet transparency material
> today, which I like for negatives but which doesn't work for beans
> for printing gum on, either front or back. So it seems to be hit or
> miss as to which brands of inkjet transparencies work for this.
>
> Katharine
>
Received on 05/02/06-08:34:12 AM Z