Re: gum curves

From: Kees Brandenburg ^lt;>
Date: 11/07/05-09:23:59 AM Z
Message-id: <>

Hi Chris,
Did you also find a relation between pigment concentration and curve
shape? I noticed that an underpigmented mix needs a lot more correction
in the curve than a higher pigmented one. So deciding on the maximum
pigment/gum ratio that does not stain and keeping that constant is also
an important step in the digital gum workflow. And different for each
colour too.


Christina Z. Anderson wrote:

> Hi all,
> Gees--subject line sounds like a sex spam for an old folks home..
> This weekend I was a curve maniac. Anything to divert myself away
> from a nude powerpoint with 265 slides to input and organize.
> A number of months ago I was working out gum curves and then I had to
> move from the South. That work just got resumed this weekend. I was
> testing, doing all my curve work with Nelson's PDN system, to see if,
> with gum, the colorized neg makes any difference over black ink only
> negs. In the past I always used the PhotoWarehouse OHP at about 1/3
> or even less the cost of Pictorico, and that accepts black ink well,
> but color puddles. Hence, monetarily I would much prefer to stick
> with PWOHP.
> One other problem I have with Pictorico aside from cost: it is such
> a thick base that it is the only substrate i have ever had problems
> with not being in contact with my paper and producing fuzzy spots. The
> PWOHP is so flimsy (and stretches, sometimes, in the printer) that it
> remains closely in contact with my paper in a contact printing frame.
> I do not have a vacuum easel :(. So if there are any waves in the
> paper from moisture or what have you, you have to watch this.
> Consistently I have found this: magenta and yellow and cyanotype all
> have different curves with both black ink only and with colorized
> inks. So I can pretty much say with surety that I will, upon
> splitting my channels for my tricolors, curve each individual color's
> neg separately. That's the charm of the PDN system is its ability to
> make custom curves--i did 6 over the weekend.
> I need mention that PDN was not designed to use black ink only so I am
> bastardizing Nelson's system (sorry, Mark)...but I figured that I
> needed to find correct curves for the black ink only negs, too, to
> give an honest comparison.
> I think I may say, too, that, oddly enough, each color's curve in
> black ink and in a colorized neg is similar in shape, but maybe not
> the same. I have no idea what this means. But cyanotype is very
> responsive to black ink only, in fact, probably too much so. And, the
> curve shape is similar with each color within the pigment family, e.g.
> cad yellow and a transparent yellow
> Today i begin printing side by sides of colorized and black negs, but
> it'll take a couple weeks to finish and post results.
> I still am planning on testing Lehman's hydroquinone hardener, but
> that'll be when I run out of my current batch of sized paper.
> Bob, so nice that you posted the stuff about grainy cyano--I have had
> that at times, too, for some unknown reason.
> Oh, it's a monday!
> Chris
> PS OHHH question, how do you deal with the areas of midtone sky that
> print out in uneven strips of density--what is that called??
Received on Mon Nov 7 09:24:52 2005

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