Re: Dots of gum?

From: Katharine Thayer ^lt;[email protected]>
Date: 02/18/05-12:45:55 AM Z
Message-id: <>

Well, this would all make sense except for one problem: it seems to rest
on an assumption that a continuous tone negative doesn't print as well
in gum as a negative made of dots, which I would have to dispute on the
basis of my own experience.

Several years ago I was approached by a colleague who was working on a
book about contact printing from large format continuous tone negatives
using various alternative processes. He wanted to know if I could help
with the chapter on gum printing, and I said I couldn't because I'd
never used continuous tone negatives. (On reflection, this wasn't
exactly true, since when I first started experimenting with gum printing
I didn't have a darkroom and a friend helped me out by lending me some
of the less important examples of his huge collection of old 8x10
negatives to practice printing with, and those printed beautifully. But
that was so long ago I had forgotten it when I talked to him, and in the
intervening years I had been exposed to the myth that says that gum
doesn't print well with continuous tone, which I repeated to him,
although I did say that I didn't know whether it was true or not).

I talked to him before I really got started with large format
negatives; had he asked me a year later I could have said with
certainty that continuous tone negatives print very well on gum and
shown him some good examples. I hope that he has gone on and finished
the book, and that there is indeed a chapter on printing large format
negatives on gum; I would hate to think I had discouraged him by
repeating a myth that is demonstrably untrue.

> > But I realized that something isn't making sense to me about this. The
> > argument has always run this way: somehow these discrete dots of gum
> > that are laid down by halftone or stochastic dot negatives stick to the
> > substrate better than gum that's not laid down this way. But here's the
> > problem I have with this argument: since it's the negative that is made
> > of discrete dots, what prints on the gum isn't the discrete dots. What
> > prints is the space around the dots. So I don't get this argument; could
> > someone make this work for me?
> Here I'm partly guessing (or surmising), and partly extrapolating from
> long-ago experience and talk with a Kodak honcho when I was testing Kodak
> lith film and developers.
> I don't think the issue is whether you're printing "dots" or their
> surround. That is, it's not the *shape*; it's the construction. A contone
> negative has unequal density (for the highlights or shadows depending on
> whether positive or a negative) that gets fainter and fainter until some
> of the marks are thin and light. That is, more "off" than "on," plus lots
> of inbetween. The fainter marks are less exposed, less substantial, than
> fully exposed, and their emulsion therefore more easily washed away.
> In a halftone negative, there are no such inbetweens. Everything that's
> supposed to be exposed is full bore; the edges, whether of the surround or
> the dot, are clear cut -- either "on" or "off," thus the partial tones
> don't handle differently (or not very differently) than full tones. In
> some (all?) halftones the thinner tones get smaller dots (or, as I recall,
> used to anyway), so that may affect printing, tho that's probably a
> footnote, not this question.
> That's my theory, anyway; if the premise is true, it's probably along
> these lines.
> Judy
Received on Mon Feb 21 12:08:31 2005

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