RE: Gum hardening: top down experiment

Yes, and my unproven explanation for the difference between unabsorbent
surface and paper is that the paper has more "tooth." I know people have
different opinions on that itself, but the way I see it is that on paper,
the hardened gum has "taller" tooth that it can grab. I don't know how to
explain this by text, but let's say we zoom in everything and perhaps we can
think of the punk-style hair (the kind that stands up). Suppose have a gum
coating on the hair, and we expose, it takes relatively little exposure to
harden from the top of the coating to the hair (if the coating is thicker
than the hair), so even if only the top part of the gum holds on to the hair
and there is unhardened gum under it, the unhardened part can still dissolve
and get out from the side, while the hardened part still has something to
grab.

For the unabsorbent surfaces, well, since you sand it, it has some "tooth,"
so it is still like the hair but with very very very short hair. If the gum
coating is thicker than the hair (especially if the thickness of the gum
coating is the same as the case above), then you really need to expose a lot
to get to the hair, otherwise the hardened gum has nothing to grab, so when
the unhardened gum is dissolved, the hardened part flakes off too.

I should repeat that I didn't perform any test to confirm this, and this
implicitly assumes top-down hardening, but it seems to explain many things
well.

Dave S

-----Original Message-----
From: Katharine Thayer [mailto:kthayer@pacifier.com]
Sent: Tuesday, April 11, 2006 1:45 PM
To: alt-photo-process-l@usask.ca
Subject: Re: Gum hardening: top down experiment

On Apr 11, 2006, at 9:30 AM, Dave Soemarko wrote:

> Well, actually even the hardened
> gum is soaked up with water at that point, so the water will continue
> to develop the surrounding gum. Sort of like if you put a piece of ice
> on jello versus you put a piece of ice on gum. The first case will
> have no problem whereas the second will make a mess.

Dave,
This makes some sense to me, and may provide a potential explanation of why
this "melting" of what seemed like hardened gum sometimes happens when
printing on unabsorbent surfaces (I've never seen it on paper, but I've seen
it on yupo as well as this experience on mylar). Perhaps when the hardened,
but still wet, gum is on a paper support, the water sinks into the paper,
leaving the hardened gum intact, but on an unabsorbent surface it has
nowhere to go so it affects the hardened gum around it.

Katharine
Received on Tue Apr 11 12:56:04 2006