Re: gum curves

Hi Christina,

Sorry for butting in but something just struck me as I was reading your
post. It was a small rock. Anyhay, my question is this (vaguely). When
you send a negative ( or a positive for that matter but more importantly
for negs), the print driver converts the RGB file to CMYK automatically.
My problem is how do you know what the component colours are in each
shade of grey and how is the transmission of UV effected for any
particular area of the print? In other woids, you get the print looking
nice on the screen, apply the curves in RGB and it looks not so nice
then you print in CMYK...And whats more does it matter??

Regards,

David H

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??
>
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Received on Mon Nov 7 08:54:17 2005