U of S | Mailing List Archive | alt-photo-process-l | Re: gum curves

Re: gum curves

On Oct 29, 2006, at 2:20 PM, Jeremy Moore wrote:

I think the only thing being meant by "better curve" is more accurate colors between the image on the computer monitor and the final color in the print, i.e. the shade of red of fingernails (in Chris's example print) match (as close as possible with the pigments used) the color they are on the computer monitor. This is how I took the initial post.
But unfortunately, that's not a valid conclusion to draw from that comparison. Were I to do the same comparison, I would be willing to bet it would come out exactly the other way around-- the tricolor gum would come out a more accurate match to the colors on the monitor, because tricolor gum (no curves) is what I do, and I can fairly accurately match colors using that method (within the limitations of pigments, as you say). But I don't do gum over cyanotype, and even supplied with perfect curves, there's no doubt in my mind that I wouldn't be able to get as good a color match with that method, because it's not the way I'm used to working. It's like I said last week: whatever you're calibrated for is what's going to come out looking best in a comparison, but it would be a mistake to draw any conclusions from that. It would be as foolish to conclude from my hypothetical result that "no curves" is better than "curves" for color accuracy (or for that matter, that cyan gum is better than cyanotype for the cyan layer, as these two issues are completely confounded in the given comparison) as to conclude the opposite from the images Chris posted.

By the same token, the comparison I posted the other day doesn't prove, or even suggest, that curves don't work. (Why would anyone even think that?) All it says it that I haven't yet found a curve that prints better than my usual way of working. But that doesn't begin to address the more general question of curves vs no curves, which isn't even a question I'd be interested in tackling. My point was exactly the opposite: that it doesn't make sense to pronounce a general rule about curves vs no curves, in either direction. Like most things in gum, it depends.

As for tricolor gum, getting an accurate color balance is about pigment and pigment concentration, about balancing the colors in relation to each other. Curves don't have a lot of bearing on that, because curves are developed for each individual pigment separately, not for how the pigments work in combination with each other. That, IMO, is why some people have reported that with PDN their tricolors turn out too dark, because making individual curves doesn't take into account that when you're doing tricolor, you need a lighter pigment concentration than you're likely to use when you are printing a color by itself. It takes less of the three colors than you might think to make a solid black in tricolor, and if you use all the colors at full strength, you're going to darken the entire print, unless you add extra development to all the layers to lighten it, or reduce the exposures, neither of which are as good a solution, IMO, as using the correct pigment concentration in the first place. You'll also end up with a cyan bias if you're not careful to balance the cyan with the other two colors, because the cyan pigment will usually be more powerful than the red and yellow and will overwhelm them if not used judiciously. But these are printing issues, not curve issues.


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