From: Katharine Thayer (kthayer@pacifier.com)
Date: 04/25/00-08:27:11 AM Z
Sorry about crossing threads here. I wanted to talk about UV light
sources for gum especially, but it was Dick's post on this thread that
is relevant to my point, although my post is really an answer to
Christina's question about what light source is best for gum.
I think Dick's got the right take on this. I've read back through the
arguments about light source on this and other lists for the last year
or so, and I haven't seen anything yet to convince me that anyone's got
the final answer on Christina's question. There are certainly people
with strong opinions on the subject, but my experience with gum
printing has taught me that strong opinions about what's best or worst
in gum printing generally turn out to be ill-advised; as Judy said,
generalizations about gum printing beg to be contradicted. For every
person who claims that a particular light source, gum, sensitizer,
paper, etc etc etc is "no good" for gum printing, there is someone else
who uses that material or equipment without a problem and to good
effect. No one variable can be considered in isolation but only in
combination with all other variables. So all any gum printer can
reasonably say to other gum printers, even after extensive testing, is:
this is what seems to work best for my particular combination of gum,
paper, negative, pigment, sizing method, weather patterns, personal
aesthetics, darkroom rituals etc etc. Your mileage may vary.
By the way, I read somewhere that potassium dichromate and ammonium
dichromate are each sensitive to a somewhat different range of
wavelengths. Does anyone know if that's true? If so, that would throw
another wrench into the effort to define the "best" light source.
It seems to me that other variables are probably more important than
light source to a satisfactory gum print. I can't remember who said it,
and I'm not going to search back through to find the quote, but someone
in one of these discussions said a wise thing: if people think that all
that's required to start producing great gum prints is to buy a
different light source, they are going to be disappointed, sometimes
after spending quite a lot of money.
So, Christina, we're not being very helpful I'm afraid. The truth is
there isn't one agreed-upon answer to your question. If it's any
consolation, I believe perfectly beautiful gum prints have been made
using any of these light sources. Although fluorescent tubes have been
roundly disparaged in some quarters, I have seen very nice prints, yes
with clear highlights, made with this kind of light.
Katharine Thayer
Richard Sullivan wrote:
>
> Ed makes some good points. When one looks at all the different processes
> and the variables involved, testing in any real sense becomes a nightmare.
> One can "test" for gum or platinum or silver and come up with some highly
> subjective judgements, but beyond that, the data doesn't mean too much.
> Even "printing speed" can vary from one process to another. I see
> differences between Ziatype and DOP.
>
> I think the best analogy as to judging the "quality" of the light might be
> in loudspeaker evaluation. You can look at the plots produced by
> loudspeakers but the quality of the sound can vary enormously and have no
> seeming relationship with the plot. Surprisingly some speakers that have
> very flat highly faithful reproduction plots sound very "unmusical."
>
> I am somewhat skeptical of the idea that some lights actually produce
> better looking prints than others. I have just heard this so many times
> over the past years that I feel there is something to it.
>
> The bottom line is that testing exposure units can give us some general
> guidelines but beyond that it can become a frivolous obsession. I think we
> all probably know a "zoney" who obsessively tests, films, developers,
> lenses, and heaven only knows, probably film holders too, and yet never
> produces an image worth looking at. Then there is the photographer who uses
> the sheet packed with the film and determines it is "cloudy bright" and
> does knockout pictures. Go figure.
>
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