Re: Adhesion

From: Katharine Thayer ^lt;kthayer@pacifier.com>
Date: 02/19/05-12:26:44 PM Z
Message-id: <421784DC.2B3F@pacifier.com>

Etienne Garbaux wrote:
>
> In my previous post in this thread, I mentioned that gum bichromate, as
> traditionally practiced, leaves unhardened gum between the hardened layers
> and the support, so it is thought (apparently with some reason) that gum
> depends on the physical tooth of a support --

I was looking for a different post of Etienne's but in looking for it I
glanced through this one and realized that I didn't read this part right
the first time. The way I understand it on this reading, I don't agree
with it.

I disagree specifically with the statement that gum bichromate as
traditionally practiced leaves unhardened gum between the hardened
layers and the support. On what information or experience do you base
that statement?

The traditional understanding, as I understand it, is that if there IS
unhardened gum between the hardened layers and the support, it means
that the gum layer is underexposed and it will wash off in the wash
water, since the soluble gum underneath dissolves and takes the
insoluble gum on top of it away with it as it goes. This makes sense to
me, by the way, although the research to establish it one way or the
other has yet to be done. But if this isn't the case, then there would
need to be another mechanism proposed to account for the fact that even
when printing on unsized paper, so that the emulsion soaks deep into the
paper, if the gum is underexposed so that part but not all of the gum
layer is hardened, whoopie, there goes the whole image unless you grab
it out of the water instantly and dry it really really fast. I don't
know how else to account for that unless by saying that the soluble gum
underneath dissolves and takes the image on top with it. However, this
makes the other hypothesis a bit problematic. If I had to guess, I would
guess a complex interaction between the two.
Katharine
Received on Mon Feb 21 12:17:04 2005

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