Actually, without knowing any better I kind of doubt that the tissue substrate
really matters very much unless for some reason it prevents the gelatin from
drying evenly. I've had success with poster board, heavy paper, and some
success with overhead transparency slides (after treating to make the gelatin
stick).
> I
>hung the tissue to dry for about 12 hours , then sensitized in
>a 3%solution of potassium dichromate, and hung and dried the
>tissue in a dark room overnight .
The length of drying time will depend on the relative humidity, and the amount
of plasticizing agents (sugar or glycerine) in the gelatine film. In my
experiments, the gelatin was often still slightly damp in spots after this
length of time. I waited about a day for the tissue to dry completely.
> The tissue dried unevenly,
>hence the paper curled and buckled badly.
It sounds like you may need to add more sugar (and/or glycerin) in order to help
things dry more evenly, but this tends to increase the time it takes to dry.
> Did I use paper that was too thick or stiff as a
>tissue substrate? Or is curling and buckling inherent when
>using paper
The buckling is caused by the gelatin shrinking as it dries. Stiff paper is
probably less likely to be as prone to this since it is harder to bend. I had
better luck with the stiffer poster board. The thinner paper substrates were
more prone to curling.
> is that why you and others have mentioned
>using film or Mylar as a tissue substrate?
It is my understanding that the plastic substrates are commonly used as
temporary supports for the cyan, yellow, and magenta images in multicolor carbon
printing. The clear plastic base makes it easier to register the image. Using
these for tissue supports doesn't seem to be as common, but is occasionally
done. One reason is that the substrate can be reused. I was also wondering
about exposing the tissue through the clear plastic base at one point.
> I have some
>"graphic arts film" ( some unsuccesful digital negs from a
>service bureau that I use) and some overhead tranparency film
>that might work, since both have a bit of "tooth" that may be
>suitable for the gelatin to adhere to.
The film would probably work since it has a gelatin layer already adhered. The
overhead transparency film will likely cause problems. I actually tried the
overhead transparency film for my first tissue support. It starts out looking
great, but as the gelatin shrinks it separates from the plastic. I did try an
experiment to pre-treat the overhead transparency to make the gelatin stick.
The resulting film stayed attached for over a month. I've posted this
information to the list before, but can give you the details if needed.
> When using film, do
>you hang it to dry or allow it to dry flat ?
I'd dry it flat on a blotter or paper towel.
> And how dry is
>"dry"? Obviously the leathery feeling tissue produced an
>image , so maybe that's what I need to shoot for.
No, I think you would be risking your negatives with gelatin this wet. What
I've used has been dry to the touch.
Hope this helps.
- Wayde Allen
(74160.3410@compuserve.com)