Re: Carbon tissue question
a.strauss@worldnet.att.net
Mon, 27 Jan 1997 21:21:51 -0500
----------
> From: Tom Hawkins <jcmjohn@ix.netcom.com>
> To: Al Strauss <a.strauss@worldnet.att.net>
> Subject: Carbon tissue question
> Date: Monday, January 27, 1997 7:11 PM
>
> Hi Al,
>
> I wondered if I may bug you with a carbon question...
>
> I tried another shot at carbon this weekend with much more success than
my
> previous attempt (at least the image didn't slide off the paper and down
> the drain) but still have a few obstacles to conquer. I believe the
> problem has to do with my choice of the substrate for the tissue and the
> extent to which the tissue must be dry before exposure.
>
> I used some crane's platinotype paper for a substrate ( had some on hand
> and I don't care for it for platinum printing) because it feels
substantial
> enough for the task. Coating went well , and 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 tissue
dried
> unevenly, hence the paper curled and buckled badly. This far into
things,
> I figured I may as well go for it.
>
> The part of the tissue that had become very dry, which I can only
described
> as having a "leathery" feeling actually yielded a decent image as I ran
> test strips for an exposure time check. But any part of the tissue that
was
> the slightest bit cool and "rubbery" to the touch (as though the gelatin
> still had some moisture content) produced no image and immediately washed
> off the final support (I used fixed put bromide paper). Of course , the
> tissue was so warped that it couldn't be flattened in the contact frame
and
> produced a mess of an image. It was rewarding , however, to see even a
> portion of an image by this point!
>
> Here are my questions: Did I use paper that was too thick or stiff as a
> tissue substrate? Or is curling and buckling inherent when using paper
and
> is that why you and others have mentioned using film or Mylar as a tissue
> substrate? 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. When using film, do you hang it to dry or allow it
> to dry flat ? And how dry is "dry"? Obviously the leathery feeling
tissue
> produced an image , so maybe that's what I need to shoot for.
I suspect that one of your problems may have been that the parts of the
sensitized tissue that were rubbery hardened from exposure to light and
thats why it didn't stick. I don't know enough about what materials you
used or proportions etc. to make a more intelligent guess.
Easiest way to make tissue is to use the graphic arts film for the
substrate. I use
old ortho negatives. I pour the gelatin onto the emulsion side. The other
side may
work as well but I have never tried it. I pour about 40ml onto an 8x10 and
spread
it over the sheet with a fine-toothed comb. Working quickly before it
cools.
After about five minutes I lift the sheet and move it to a piece of
cardboard and tack
it down. I leave it horizontal and never lift it until I am ready to use
it. Therefore it
never gets a chance to curl. I let it dry overnight. It should then be a
thin dry film
on the tissue. No sponginess at all. I do not sensitize the tissue until I
am ready to
use it. The sensitizer I use is 3 gm potassium dichromate + 50ml hot
water. I then
add 50ml of acetone to help it dry quicker. I spread it on the tissue with
a foam
brush brushing both horizontally and vertically. Five minutes later I give
it a second
coat. I then dry the tissue using a hair dryer held at a distance so that
there is just
a mild flow over it. In five minutes it is completely dry and ready for
use.
What is the final receiver paper that you are using? Is it sized ?
Hope this helps
Cheers
Al