Re: Gum, newbie questions

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, November 17, 2005 10:22 PM
Subject: Re: Gum, newbie questions

Hi Yves,
I feel your frustration, but iIt might be easier to help if you could
simply describe the results you're getting, in as much detail as
possible, then we could address the problem more specifically.

****************
I think my Gum problem(s) question give more details and is more specific.
****************

I've intended, since I put up my website three (?) years ago, to add a
troubleshooting page showing visual illustrations of specific kinds of
failures and the solutions most likely, IME, to cure the problem, but I
haven't had time to do this yet.

******************
That would be great.
******************

In the meantime, let's address the problem of the emulsion floating
off, which is one specific problem you raised. If the emulsion
"floats off" as a film, in other words if there in fact is a hardened
gum layer that leaves the paper and floats off, either as a lovely
intact veil of colored film wafting hearbreakingly through the water,
or as a lot of shards or flakes of colored film, then the problem could
be too much sizing (although from your sizing question earlier, I'm not
sure you're sizing at all, in which case this wouldn't be your
problem) or too slick a surface (this happens for me a lot with yupo or
glass)--- or too thick a coating. But if the emulsion washes away as
a liquid, in other words if you see color going into the water like dye
rather than like a veil of film, leaving no image on the paper, then
the problem is almost certainly simply underexposure: the exposure
hasn't been sufficient to create a layer of hardened gum at all.

As to whether the upper portion of the emulsion hardens first and can
be washed away by the insoluble gum underneath, this is one of the many
controversial issues in gum. One alt photo personage has a theory that
dichromate ions gravitate to the paper, and therefore hardening
actually takes place mostly at the paper surface and below, rather than
higher in the emulsion. I have some questions about that theory, but
won't go into them here, and besides, without some kind of microscopic
analysis, it's impossible to know which is right, so it's one of those
discussions that don't yield any practical help for the beginning gum
printer.
***************
I'm not saying the theory of this personnage as you say is right or wrong
but what he is saying implies that somekind of force is driving those ion to
the paper and it must be very strong and its interaction must be working at
relatively long distance. Let just say that there is a well known theory
(entropy) that says his theory is most probably false, kind of gazillion to
one. I'm not a scientist which is another way of saying I could be dead
wrong but the only force that can move ions around would be electric and I
don't see, even in the presence of metallic pigments, that an electric
current would flow somehow in this stuff
***************
While I think your reasoning is sound, theoretically, about the role of
the thickness of the emulsion interacting with the opacity or
transparency of the pigment, I'm not sure that's a really fruitful path
to take in terms of getting quickly to good gum prints; at any rate it
hasn't been my experience that practically it makes enough difference
to worry about. I guess it depends on what you want. I think the
answer to this question would be useful to gum theoreticians, if there
indeed be such folks, but I'm not sure it would be the fastest way to
get yourself to printing gum, if that's what you want to do most.
**************
Yes I kind of wandered a bit if not a big bit, probably the frustration like
you said.
**************
Not sure you'll find any of this helpful, but it's what comes to mind.
At the moment, I'm very tired after spending the day out shooting, so
might have some fresher thoughts in the morning.
Katharine
Received on Fri Nov 18 07:34:47 2005