Re: Could someone summarize that gum up or down discussion?

> Judy and Chris mentioned the fact that unreacted dichromate leaves the
> print very rapidly, as an observation supporting bottom hardening, but I
> don't see bottom hardening as a necessary conclusion from the
> observation. The hardened gum matrix is a net rather than a solid slab,
> and the dichromate can easily slip through the net, at least that's the
> way it was explained to me by a physical chemist. So the observation that
> the dichromate runs out easily is neither here nor there as far as which
> way gum hardens, IMO.

Whhhhoooooaaa leave me out of this.
I never said that as a "support" of bottom up.
In fact, all I said was a "this is verrrrry interesting" remark when you,
Katharine, mentioned Mike Ware's theory of bottoms up, by remarking that
sometimes I observe when brushing on a layer the dichromate seems to be
separate and at the bottom of the brushed swathe.
SO, for the record:

1. I could actually care less whether gum hardens top down or bottom up.

2. The practice of exposing from the back of the paper is as old as the gum
process and came about when the prevailing thought was that gum was
incapable of producing halftones and then led to carbon printing in general
(crass historical generalization).

3. The reasoning behind the original old practice of presensitizing the
paper with dichromate and then brushing on a nondichromated gum layer was to
keep the dichromate at the surface of the paper where it would harden the
gum in contact with it at the surface where it would then not only adhere
better to the paper (no slough off) and also be faster printing (did not
prove to be true), was, in fact, another reasoning to support top down
hardening.

4. I just don't personally see any reason in my gum practice to worry about
this, not having an inability for a layer to adhere to the surface nor
having lack of contone in my layer.

But hey, I just went through 2 days of intense job interviews so this issue
seems pale by comparison, and as far as I am concerned a cold beer is in
better order...Chris
Received on Thu Apr 13 21:26:51 2006