Re: Adhesion

From: Katharine Thayer ^lt;[email protected]>
Date: 02/18/05-12:20:19 AM Z
Message-id: <42158913.25A6@pacifier.com>

MARTINM wrote:
>
> I'd guess the silane doesn't care whether the gum is crosslinked or not and,
> it won't have any effect on the crosslinking.
> It simply adheres to both glass and gelatin (or gum, hopefully), making a
> close bond between the two.

I think maybe we're talking past each other, Martin. Maybe we're saying
the same thing but not understanding each other. Let me give another
stab at what I'm trying to say, and see if we can get any closer.

The gum process requires that the gum that's not exposed, that's still
soluble, must be free to leave. I'm sure you must know this, so I take
it you're saying that this close chemical bond between the silane, the
glass, and (theoretically) the gum would be loose enough to allow the
soluble gum to be released while at the same time it would hold the
crosslinked gum tight to the glass?

There's only one way to determine whether silane works for gum, of
course, but since there are about 27 different silanes and I don't know
which would be a good one for gum (although I concur with you in
wondering whether the ones that work best with gelatin would work well
with gum, since the groups available for bonding are different in the
two cases) and since I'm dealing with only two things right now: (1)
pain and (2) these two group shows coming up, this will have to be
tabled for later, unless some gum printer other than myself is willing
to take it on as a project. Since I do know how to adhere a gum image to
glass using the principle of tooth, I will continue on that path for the
time being.

In my opinion the quality of getting dissolved
> by water has nothing to do with adhesion. That mainly depends on the degree
> of crosslinking.

I agree, to an extent, that the quality of being water soluble has
nothing to do with adhesion. Using the distinction I made earlier
between the adhesion of the wet gum coating to glass and the adhesion of
the crosslinked gum to glass: the wet gum coating adheres well to glass,
in my experience, even though the coating when dry is completely and
highly water soluble. And the fact that the soluble gum adheres well to
glass has no relation at all to whether the crosslinked gum will adhere
well to the glass. As I keep saying, if there's tooth, the crosslinked
gum will stay; if there's not, off it goes. So certainly, adhesion is
not related to solubility.

But still, there's this problem that the gum has to stick only where the
image is, and has to not stick where the image isn't, and that's the
problem that I have with the idea of the adhesion of gum to substrate
being a question of chemical bonding. It seems to me that either it
would bond the gum to the glass entirely, in which case you would get no
image because the entire glass would be covered with pigmented gum, or
it wouldn't bond the gum to the glass at all, in which case you wouldn't
get an image for a different reason.

If it can be demonstrated that the silane somehow provides that physical
"tooth" or even a chemical tooth which will allow the crosslinked gum to
hang on but the uncrosslinked gum to let go, in the same way that paper
fibers and grit and roughed-up plastic keep the crosslinked gum and
release the soluble gum, then certainly I'd have to be convinced, but
I'd have to see it to believe it, and I'd still want to understand the
mechanism of how it would work.

> Consider the situation when dealing with a silane subbed glass plate. The
> tiny silane layer firmly adheres to glass (actually, it's very difficult to
> remove it again). At the same time it provides (what you previously
> called )"teeth" for the gelatin (gum)...

Actually, I have not stopped calling "teeth" "teeth." Anyone who thought
he had convinced me that "tooth" is not a useful construct to describe
the "adhesion" of crosslinked gum to a substrate would be quite
mistaken. As I've explained several times, what I've seen demonstrated
again and again in my own practice and experimentation, is that tooth is
everything when it comes to affixing a crosslinked gum image to its
substrate, "tooth" being any physical structure (paper fiber, grit, any
surface roughness, perhaps a crystalline structure (although that last
part so far is pure speculation on my part) that the gum can
incorporate into itself as it hardens and by that physical handle hold
itself to the surface.

Katharine
Received on Mon Feb 21 12:08:06 2005

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