Re: Two methods of sensitizing for Direct Carbon

Good Morning!
Hope springs eternal when Spring Break arrives! More like Spring Catch Up
for me...

Gum could be precoated with gum/pigment and then sensitized with dichromate,
by floating or by brushing (brushing with methyl alcohol in place of half
the water, too). This was talked about even until the late 30's.

The preferred method for quite a while was presaturation of the paper with
the dichromate solution, which would not go "bad", and then coating the
paper at time of use with the gum/pigment mixture. They thought it was 2/3
of a POP exposure time, and if mixed in with pigment it was 2x POP exposure
time. They also thought it produced cleaner whites. Most writers of the
time agreed with this except for several, who would state, "So and so said
such and such but I have not found this to be the case". It was noted in
one book that if the paper was heavily sized, the presensitization would
deteriorate, which certainly would stand to reason since starch can be used
to print with as well as gum, glue, etc. This method was in the literature
at least until the late 20's.

Since speed seemed to be the benefit to this method, I can imagine it had
its heyday. Maybe the speed increase could be attributed to the interaction
of the dichromate with the paper sizing, in essence starting a dark reaction
going before the exposure of the negative. If there are other benefits to
having to do essentially an extra step, that's what I'd be interested in.
But my guess is there aren't, so that's why it fell out of use with the next
resurgence of gum in the 60's/70's.

This summer I hope to test this method against the norm and see if there is
any dif, but the fact that my diginegs print in 4 minutes does not make
speed an issue for me.
Chris

----- Original Message -----
From: "Judy Seigel" <jseigel@panix.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, March 13, 2004 8:53 PM
Subject: Re: Two methods of sensitizing for Direct Carbon

> On Sat, 13 Mar 2004 Grafist@aol.com wrote:
>
> > One. For Direct Carbon which resembles the gum process the sensitizer
> > is mixed in with the colloid on coating. Am I correct in assuming that a
> > pure gum + pigment coat cannot be sensitized after drying....the gum
> > would be washed away by the dichromate? (Judy ??)
>
> They say that John, just like they say a lot of other things. But not so.
> You could make the dichromate solution very cold, so that by the time it
> started to dissolve the gum it would be done -- before exposure anyway
> it's not so serious if you have a little blurring; it dries solid again.
>
> Another way would be to spray the dichromate solution on (as shown in a
> couple of articles in the teens), or even (maybe I'm inventing this but it
> could probably be done) saturating a mat or paper of some sort & laying it
> on.
>
> But what WAS done fairly often was sensitize from the back. I don't
> remember if that was done with another sheet or by floating in the
> solution or by brushing the solution on from the back (buckle brush) --
> probably all. So the answer to your question looks like not so. I'm
> having a vague memory now also of something in one of the old books (Photo
> Aquatint? One of them...) about a big discovery of applying the gum &
> sensitizer separately and finding it was a lot faster, but then in the
> next chapter they took it back; it wasn't faster after all.)
>
> But I'd bet one million (no, make that two million) dollars the idea that
> it COULDN'T be done was used as rationale for something else.
>
> J.
>
>
>
Received on Sun Mar 14 08:33:49 2004