FOTAR2@aol.com
Date: 07/30/03-09:53:00 AM Z
Since this process has been mentioned a few times on the list, I thought I
would publish it in it's entirety for those who may not have stumbled onto the
preliminary version on Dick Sullivan's website. Hopefully it will prove of use
to some of you. I had given that earlier version of the entire procedure to
Sandy King for use in his book, but have not had a chance to see any
refinements he may have come up with.
As I learned by making my own Ferric Oxalate starting with steel wool,
while it's nice to know how to roll your own, storebought lets you get on with
it.
HOME GROWN CARBON TISSUE
Here is yet another approach to making your own carbon tissue. It is
strictly about the mechanics of getting the gelatin onto the paper. I’m not going
to deal with any formulations of the gelatin matrix, though I do like to
incorporate the Bichromate directly into the tissue thus eliminating the step of
having to sensitize it later. There are extensive listings of formulas available
through the carbon website.
Magnetic sign material is available (1) (Hereafter referred to as the
mask) into which it is easy to cut out a window the size of the patch of
gelatin you want to lay down. Before I cut out the window, I cut the original
magnetic sheeting so the the outside dimensions are larger than the overall size of
the paper to be coated. That way you can't spill any gel onto the outside
edges of the paper. You will need a sheet of iron (2) for the mask to adhere to.
It should be heavy enough to give the mask something to be attracted to, to lay
flat and, if possible, it should be firmly attached to a perfectly levelled
surface if you want your tissue to be of a uniform thickness.
First soak the paper. I use Bristol two ply paper and soak it in hot
water until I can easily peel the plies apart. This leaves 2 very thin sheets,
each of which already has one side with a nice gelatin coating for your gel to
mate with. Place the paper lightly, (in the case of the Bristol - gelatin side
up) onto your iron sheet. Don’t squeegee the water out of the paper before you
lay it down, as you want the the wet paper to cling to the iron sheet - once
it is down, smoothed out and positioned properly, you can squeegee off the
excess water firmly but lightly, so the paper lies dead flat. (I use the window
washer’s type of squeegee - very professional) It helps if you can attach some
kind of shoulder at the top edge of the platen that you can use as a stop to
aid in the positioning both the paper and the mask. Now lay the mask down onto
the paper with a kind of rolling motion so as not to disturb the paper. The
mask will adhere to the iron through the thickness of the paper with enough
force to keep the gel from sneaking underneath. I’m not sure how that would work
with thicker paper as I have always used the Bristol, but I suspect others will
work as well. For 8x10 work, I lay down a patch of gel which is 10x12” on an
11.5 x 14.5” sheet of paper. the 10x12x.032” cavity comes out to a volume of
about 63 ml. but I use 70-75ml to give myself some slack.
Pour in the heated gel (~ 125 degres) with a plastic grease separator to
minimize bubbles or other detritus. First pour the gel into the corners of one
end of the well formed by the mask - then let it all flow in, distributing it
along this “top” edge of the paper as you go. The next and perhaps the most
important step is to use a polished round iron (preferably stainless) rod as
another sort of squeegee (slide it, don’t roll it) to move the puddle of gel
into the rest of the well. The one I use is 1 1/4” in diameter and about 16”
long, mostly because that’s what I had, but it turns out to be a good choice. By
being that rigid, it has no tendency to sag and intrude on the .032”
clearance provided by the mask. Being quite heavy, It has a lot of thermal mass, so by
getting it good and hot (~130 degrees ) the rod is able to continuously keep
the top surface melted where they meet, keeping it from gelling prematurely,
or remelting it if it is starting to stiffen up. With practice, you should be
able to distribute the stuff nicely with just a few passes of the rod. The
heated rod enables you to go as slowly as necessary in order to keep the gelatin
from piling up in front of it and going over the sides. Let that happen when
you get to the final stroke to get rid of any excess. This also has the
advantage of getting rid of THE problem - bubbles. when you do it right, the surface
of the gel will look mirror smooth right to the edges. I’m lucky enough to have
an old proof press with a 400 pound cast iron top. This makes a great
heat-sink, so that the gelatin sets rather quickly for as many sheets as I want to
pour. The nearer you can come to emulating that configuration, the better off
you will be. As soon as the gel has set, gently slice the edges of the mask
opening with a toothpick or its equivalent, and peel up the mask. Don’t push the
toothpick so hard that you cut into the paper, you just want to release the
gel from the edge of the mask. Let the tissue continue to cool until you are
certain there aren’t any parts that will slump, or run if you hang it up to dry,
then remove it and dry it.
Some observations:
I heat up my gel in a microwave oven, making enough for as many sheets as
I plan to coat. Then I reheat it again between pours. That works for me, but
I suspect some kind of continuously heated tempering bath would be preferable.
Even though the mask thickness dictates a .032” depth, you should be able
to modify the final thickness of the dried coating by varying the percentage
of gelatin in the gel.
Be careful to wash the mask thoroughly between pours, especially when it
comes to melting off all the overflow gelatin. Little bits of even
semi-hardened gelatin can screw things up in a hurry. I use a mild scrub brush with hot
water.
When you are cutting he window in the mask, be very careful at the
corners or it can tear. (you are handling it in ways that it was never intended for)
Until you are practiced at eyeballing when you’ve poured out 75ml. try to
find a lightweight plastic cup that holds the right amount. Don’t use
anything heavier unless you’ve heated it beforehand or it might tend to make the
stuff gel prematurely.
You have to be pretty judicious about keeping the iron sheet clean and
dry, it will rust at the least excuse, right in front of your very eyes. I never
had that problem with my press so I never fixed it. If I had to fix it, I
would try immersing the entire sheet in a fairly strong solution of copper
sulfate. I vaguely remember doing that one time by accident and getting a rather
nice thin, copper plating on the steel. Check with one of the resident chemists.
Don’t even think about stainless, it’s nonmagnetic.
The main thrust of this paper is to bring to light the combination of the
magnetic mask and the steel plate - probably the biggest benefit being the
reduction of the bubble problem. The same approach may have applicability for
other processes that require coating gelatin onto paper. The reason for writing
the paper, is that as soon as Dick Sullivan gets his tissue on line, I’m not
going to bother doing it anymore, and I thought I’d like to record it before it
disappeared into the dimmer recesses of my mind. Maybe it will come in handy
for someone out there. I know I spilled a lot of gelatin till I came up with
this approach. Now if you think that I have a bunch of carbon prints laying
around . . . well, I actually worked out the technique in order to be able to
make my own carbon tissue for photogravure resist, which is basically a carbon
print on copper.
Bob Nugent
1.) Dick Blick (www.dickblick.com) sells it by the running foot, 12” or 24”
wide, and it was $4.45 per foot when I got mine.
2.) Graphic Chemical & Ink Company (www.graphicchemical.com) sells 18ga.
Steel Engraver’s Plates which are highly polished till the first time you breathe
on them. They are reasonably priced. (12x18” @ $6.05 last time I looked.)
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