U of S | Mailing List Archive | alt-photo-process-l | Re: Re: separations for gum printing

Re: Re: separations for gum printing

Interesting to read the discussion on curves. My own engagement with the 
PDN process was mostly motivated not by any desire for a photo-realistic 
gum print, but rather a search for consistency in gum printing. I only get to 
print a few times a year, and I was fed up with reinventing the wheel or 
making the same mistakes every time - so a process which pinned down 
several variables while providing a lab-notebook reference for the future was 
what I needed to avoid quite so many discarded prints. For that it has worked 
admirably. Now it's possible to experiment with pigments ("what would that 
look like with venetian red, egyptian blue and yellow ochre?") with the other 
variables a bit more under control.

On the other hand, I don't think the term "photorealistic" really applies to a 
gum print in any case, even one with "ideal" pigments, curves, and the whole 
works. A gum print is just a whole other kind of object.

best wishes


> From: Katharine Thayer <kthayer@pacifier.com>
> Date: 2008/11/20 Thu PM 11:30:08 GMT
> To: alt-photo-process-l@usask.ca
> Subject: Re: separations for gum printing
> P.S.  I went back and reviewed all my information about curves;  it's  
> interesting to note that only these particular (rather intense)  
> mixtures for tricolor have that particular shape.  Less concentrated  
> mixtures of the same pigments yield curves that are very close to the  
> straight diagonal line.  I think I said this somewhere else in the  
> last few days, but what I found in my exploration of curves for gum  
> is that the curve shape seems to be related largely to the pigment  
> mix (not absolute pigment concentration, but the color saturation  
> relative to that particular pigment) rather than to the hue range.
> At any rate, the steepness of the curve at the dark end of those  
> particular curves for those particular tricolor mixes seems to serve  
> the tricolor print well, promoting good open separation in the  
> shadows, and I don't see any particular reason to fret about it.
> One correction:  I said thalo was the cyan pigment in that group that  
> I provided the curves for; actually it was Prussian.  I can't find a  
> curve for thalo, and am not sure I've ever done any calibration for  
> thalo.  It's not my favorite blue pigment for tricolor.
> Katharine
> On Nov 20, 2008, at 1:00 PM, Katharine Thayer wrote:
> > Unlikely, Mark, on either point:  overexposure (since my exposures  
> > for these were well established by step tablet, as explained in a  
> > separate thread and on my website page covering exposure for gum,  
> > and besides, by any objective criteria a 2-minute exposure with a  
> > photoflood bulb is unlikely on the face of it to be overexposed) or  
> > too dense a negative (since my negatives are so thin I have to put  
> > something white behind them to tell even what the image is, and the  
> > color I use for the negatives, determined using Michael Koch- 
> > Schulte's RNP Arrays, seems to work very well).  I showed one of  
> > these negatives a couple weeks ago for someone who was interested  
> > in what film I use for my negatives; it might be useful to show it  
> > here.
> >
> > http://www.pacifier.com/~kthayer/html/orangeneg.html
> >
> > I suspect the shape of the curve has more to do with the nature of  
> > the gum mixes and  and of the way I like to print than of anything  
> > else; if you can find something to criticize in my actual gum  
> > prints, then we can talk about it, but just criticizing the curves  
> > in the absence of the prints seems, well.... sort of beside the  
> > point, if I might say so.
> > Katharine
> >
> >

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