Dichromated hardening of gelatin size

Last June I posted a couple of tests that showed that unhardened gelatin
size becomes hardened, presumably by the dichromated colloid process,
wherever exposure occurs in the gum printing process. They can still be
seen at

http://www.pacifier.com/~kthayer/html/Current2.html

The first test didn't show up the effect very well in the jpeg, so I
repeated it in a different way to make it more obvious, but left the
first one on there anyway.

At the time, I was arguing that it shouldn't be absolutely necessary to
harden the gelatin size, because if there is tone throughout the image,
the exposure will harden the gelatin, and if there are areas that are
paper white, you can wash off the unhardened gelatin with hot water so
it doesn't invite bugs later.
Katharine Thayer

> >>> rs@silvergrain.org 12/21/04 10:53 PM >>>
> > ...Also, dichromate diffused from your gum layer to the sizing layer
> can
> give the gelatin size an additional hardening effect if the area is
> exposed. Chromium (III) is a more effective hardening agent than
> aluminum ion.
>
> So, what you described naturally leads to a question what happens if
> you increase the degree of hardening to the gelatin sizing layer.
>
> --
> Ryuji Suzuki<
>
> That's exactly what I'm suggesting and pondering based on my recent
> observations. I've not read about this additional hardening effect in
> the standard texts on gum nor do I recall the topic of chromium
> hardening of gelatin being discussed on this list.
>
> Joe
Received on Wed Dec 22 07:21:47 2004