Re: gum curves

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.

kees

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