U of S | Mailing List Archive | alt-photo-process-l | (Drumroll): gum prints w curved vs uncurved negs (Re: How many gumlay

(Drumroll): gum prints w curved vs uncurved negs (Re: How many gumlayers (Re: ferri sesquichlorati)

Okay, I've posted a gum print made with a neg (from ChartThrob) geared to fit my emulsion and printing conditiions, next to a print made from the same file, no curve.

I printed several templates and generated several curves from the same emulsion last night, because being a statistician, I needed to convince myself that the curve for a particular emulsion would be reliable and robust (in other words that minute variations in how I mixed the emulsion or coated the paper or whatever would not skew the curve; this seemed to be the case, in other words the curve does seem to be robust to unessential differences. But I used up so much emulsion printing those templates that I had to mix up some more pigment mix this morning, and so I printed another template and generated another curve this morning for the new mix. Even though it was essentially the same mix, I wanted to be sure that the curve I was using was generated for the exact mix I was using. Again, the curve looked very much the same as the other curves.

I made sure that I had the positives and negatives straight (his directions and labels are helpful in that regard) and the "corrected" file looked very much like his example of a "corrected" file, so I don't think I did something really stupidly wrong, but if I did, someone can tell me.

The curve is not a drastic curve, and the two negatives differ from each other not at all drastically, but I could tell just by looking at the corrected negative that it would print flatter and darker than the uncurved one, and so it did.

Both prints and all the templates were exposed at 2 minutes, but I developed the "curved" print an hour longer than the other one (if I'd developed it the same amount of time as the other one, it would have looked even worse by comparison, but I wanted to give it every chance of turning into something, so I gave it some leeway).

I spent something like 8 hours of my time and a bunch of paper and transparencies to end up with a worse print. I don't get it.


On Oct 25, 2006, at 10:28 AM, Ender100@aol.com wrote:

Hi Katherine,

Whatever works for you is the way to go.


In a message dated 10/25/06 10:50:56 AM, kthayer@pacifier.com writes:

>  " Otherwise, why not just start with an image, invert it and make
> a negative of any unknown density without a curve and keep fiddling
> with it until you get what you want in the print."
> Best Wishes,
> Mark Nelson

Well, indeed, why not.   Like Keith, this is exactly my approach and
as Keith says, it works fine.  And as Chris showed last week, it
works good for her too.  Her tricolor gum made from inverted uncurved
channels was cyan-biased, but that's not a function of the curves,
that's a function of the  selectiion of pigment concentration of the
three pigments in relation to each other.  So I guess my answer to
Mark's question "why not?" is,  beats me!  Seems like a perfectly
reasonable approach to me.

But since Charles posted the link for ChartThrob yesterday, I've been
playing around with generating curves some myself, and like Keith, I
have to say, so far I like the "no curve" approach better too.

Recently, Mark, you said that a beginner could save a lot of time,
money, and materials by investing in a system for generating curves,
or better yet, two systems.   At the time, that didn't make sense to
me, because the time and materials you "waste" in the beginning
learning to print gum are "wasted" in the process of learning to
print gum, not in the process of generating negatives, and you still
have to learn how to print gum, no matter how you generate your
negatives. So I'm not sure how it would make any difference.   And
besides, the way gum works, there's very little waste; there's almost
no print that can't be salvaged; pigment stain is the one exception,
and curves or no curves don't have any bearing on pigment stain
But I didn't think there was any point in arguing further, so I let
that thread die without saying so.

But now, after an evening of printing value templates,  I have to say
I think the savings are in the other direction; you save more
materials by printing gum. At least when you're actually printing
images, you have a print to work with and do something with, and
chances are you can do something with it, even if you didn't get it
"right" on the first printing.  But a template of value patches is
just a template of value patches.  And if I was really going to do
this, I'd have to do it for every single different pigment I ever
use, at every concentration I use it at, at every environmental
condition (humidity, particularly)... I would be doing nothing but
printing templates for the rest of my life, and there's not a thing
you can do with the stupid things, except generate curves.  Talk
about waste of materials!  I'd rather be printing gum.

I can't say yet whether the resulting curves would be an improvement
over the uncurved negatives; I'm not even there yet  Will report in
due time with a comparison.