Re: Adhesion

Thanks, Martin, it took me a while but I think I've got it now, how it
probably works. For some reason I couldn't get past the idea that it
would affect the whole layer. To me it seemed to make about as much
sense as mixing glyoxal, say, with gum and then expecting it to behave
differently in the different tonal areas. But I think I'm on track now.
Thanks again,
Katharine

MARTINM wrote:
>
> Sorry to send this message once more - I already sent it yesterday but it
> didn't seem to have been posted to alt.photo...
>
> > 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?
>
> Just a guess but I assume the situation of a silane/gum coated glass will
> not greatly differ from that of a gum coated paper.
> Maybe we ought to consider a photo layer (say, a "normal" silver halide
> layer, dichromated gum, photopolymer etc.) as a three-dimensional
> structure -
> even if it's a few um thick only. Its surface is likely to behave
> differently from those parts closest to the substrate.
> If that particular silane ( 3-aminopropyltriethoxysilane) really behaved the
> way I believe, the only relevant region would be where gelatin/gum gets in
> contact with the glass. I assume this to take place on a "sub"-nano level
> AND NOT throughout the whole layer thickness.
> But as you already pointed out, unless someone tried... Well, at least with
> gelatin it works.
>
> Martin
>
> ----- Original Message -----
> From: "Katharine Thayer" <kthayer@pacifier.com>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Friday, February 18, 2005 7:20 AM
> Subject: Re: Adhesion
>
> > 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 12:18:18 2005