Re: gloy for tricolor on yupo?

On Mar 31, 2006, at 9:07 AM, Loris Medici wrote:
>

>
> L> But what makes you think: the PVA which adheres perfectly to the
> L> substrate before exposure should (or may) loose that property when
> L>hardened?
>
> K>"Well, goodness, I don't just "think" that;, I know it from much
> experience coating glass and yupo and mylar with nice smooth even
> coats of gum that "adhere" to the substrate beautifully but then in
> development the hardened gum floats off into the water. This
> knowledge that the adherence of the coating and the adherence of the
> hardened gum are two different issues is a product of experience, not
> just a speculation."<
>
> Have you put the coated paper in water before exposing to see if it
> sticks better than when unexposed?
>
> Yes, I know it's an incredibely silly question. I'm just trying to
> explain my point in the original question - you simply can't draw a
> conclusion such as "adhesion of hardened PVA is less than unhardened
> PVA" by developing prints in water. You have to test without using
> water
> to say something like that. It's perfectly fine to say "x type of PVA
> doesn't adhere to Yupo after exposure, when developing", that will
> show
> us it's not a fine binder for using on Yupo - that's all, it won't
> tell
> us about the before and after exposure adhesion properties.

But I think you're doing what I was doing to you yesterday: reading
something I didn't write. I'm not claiming anything about before and
after exposure adhesion properties of colloids. I didn't claim that
"adhesion of hardened PVA is less than unhardened PVA;" this
statement doesn't even make sense to me. What I said was that in my
experience printing gum on hard surfaces, whether the gum coating
adheres to the surface is a different issue than whether the hardened
gum adheres to the surface. But I'm not claiming even for gum that
the adhesion of hardened gum is *less* than the adhesion of
unhardened gum (perhaps I didn't make it clear enough that the
hardened gum doesn't float off the glass in development ALL the time,
just some of the time; I'm not claiming any relationship between the
two issues in either direction, um, except for the obvious and
trivial fact that if the coating doesn't adhere to the surface, there
will be nothing there to harden ) and I'm not claiming anything at
all about PVA, since I've never printed PVA on hard surfaces.

All I'm saying is that in my own experience printing gum on hard
surfaces, the two issues: (1) whether the coating adheres well to
the surface, and (2) whether the hardened gum adheres well to the
surface after developing, are two different issues. Having said they
are two different issues, I am not claiming to know any relationship
between them (except of course for the obvious and trivial one that
if the coating doesn't adhere to the surface, there can't be any
hardened colloid to adhere later) and I am especially not saying that
I think the hardened gum has less adhesion than the unhardened gum;
I hope that's clear.

As far as your proposal to put the coated substrate, unexposed, into
water to see how well the coating adheres--- perhaps I'm not
understanding the suggestion exactly, because this seems nonsensical
to me as posed. You say it's an incredibly silly question, well, it
seems to me that it is. Because the underlying principle of the gum
process, the principle that allows for the development of an image,
is that the unexposed emulsion dissolves when put into water. So it
seems to me that by definition any substance that would work in a gum-
like process, when coated onto glass or mylar or paper or whatever,
should dissolve from the substrate when placed unexposed into water,
and that certainly has always been my experience, that it does.
But I've only ever printed with gum. So I'll ask another question:
does temperaprint stay glued to the yupo when put into water
unexposed, and if so, how does one develop an image?

  I applaud Gord's and other's efforts to find the perfect colloid; I
look forward to the result. But my own experience and understanding
of the process tells me that anything that isn't soluble in water
when coated and dried but not exposed (for example the polyvinyl
acetate glue that I once tried using for gum printing by mistake)
cannot, by definition, be a good candidate for a gum-like process.
But maybe I'm not understanding how different these other colloids
are from gum, in which case maybe it doesn't make sense to discuss
these processes as if they were all closely related. Or maybe the
distinction you're making is subtler than I'm imagining.

I'll answer your other questions, about the Bolte paper, later,
Katharine
Received on Fri Mar 31 12:26:58 2006