Re: Help with what I believe is a hardening issue

gdimase@hotmail.com wrote:
>
> Hi Katharine,
> Then, how do you theoretically explain when you print gum on top of glasss
> or alluminum?
> If you don't size it you can't get the image on the gum.
> Glass and alluminum are perfectly clean without any "tooth" and you can
> print perfectly on them, right?

Umm, have you tried, yourself, printing on glass or aluminum? I haven't
found it so easy, and it's my understanding that even the people who
have mastered printing on these substrates (Galina, Keith, for two) have
put some effort into it. They can speak for themselves, but I certainly
wouldn't say so confidently that one can "print perfectly" on glass or
aluminum, just like that. My understanding is that people prep the
surface various ways, sub it with various materials, etch it, sandpaper
it, overexpose to kingdom come (although I didn't find that helped in
my own case) sometimes incantations, to get around the very real
problem of no tooth on these surfaces.

An example from my own recent experience that might help illustrate the
difference between tooth and no tooth: I needed to expose gum on a
nonporous surface, for reasons that aren't important for this
discussion. In spite of all advice and effort, I was not able to
reliably retain the gum on glass through the development stage (because
of the nature of my task I couldn't sub with any chemical nor could I
use a size) so after a couple days I gave up on glass and turned to
mylar as a substitute. The mylar out of the package was as bad as glass,
but I found that if I scuffed it well with sandpaper, it worked like a
dream. What the sanding does is make scratches, hills and valleys and
ridges in the mylar, in other words, "tooth" for the gum to hang onto.
But if I filled up that tooth with sizing, then the mylar would again
have difficulty hanging onto the gum.

>From Christopher James' section on printing gum bichromate on
alternative surfaces: "Tooth is the surface texture of the substrate and
is what's needed to hold onto an emulsion or image once it is printed.
To create tooth, take your pick of a number of techniques. Acid etching
of metal, sandblasting, steel wool, power sanding, multiple coatings of
gloss spray paint, or any other way you can think of putting a texture
on whatever you are using for a printing surface." Then he goes on to
tell in detail how he creates tooth on metal plates. I don't always
agree with Christopher James, but at least on this issue he and I seem
to be inhabiting the same gum universe.
Katharine Thayer
Received on Fri Nov 12 23:11:23 2004