[alt-photo] Re: 3 color gum and PDN calibration?

[Diana Bloomfield]

Hey Johnny,

I'll just say first-- that there are many more people on this list who have more years of gum printing behind them than I do, and each of us probably has our own ideas and ways of printing, but I'll just offer what I've found works for me.

I just taught a private gum workshop a couple of weeks ago, and the first thing the woman wrote to me-- after she got home to try it on her own-- was that she had problems with the blue layer.  I think her specific issue was just over-exposure.  She was using the sun, and down here in the sunny Southeast, the sun is actually more intense than my UV print frame we were using.  

At any rate, I tried a lot of blue pigments, and they each had their own (bad) issues.  In my experience,  Prussian blue (M. Graham or Daniel Smith) really worked the best.  No staining at all-- which isn't true with some of the other blue pigments I tried.  I also try not to be heavy-handed with it, and-- in the end-- if I need to darken the shadows, I'll just go back over with blue again.  I'd rather do that, than run into staining problems and/or things just getting muddy.  Typically, my exposure time for the blue layer is around 4 minutes, using a UV vacuum print frame.

I know that some people here use cyanotype for the blue layer, rather than a watercolor pigment.  I find the cyanotype layer a little too rich or intense for my images, so I don't use it-- but that's a smart way of getting around the blue pigment issues.  I'm guessing that the cyanotype layer (rather than pigment) would probably make the image a little sharper, or more defined, too-- if you like that sort of thing.

I use Arches Platine for platinum/palladium printing, but I tried it for gum printing, and I did not think it worked at all well.  I now use-- based on suggestions given here on the list-- Fabriano soft-press paper, which I don't even have to size or pre-shrink.  I have printed as big as 16x16 without sizing or pre-shrinking.   It's like a dream, really.  I've used this paper with at least 5 layers, and no staining at all.  I just hope they keep making it and don't change what goes into it.

Okay, so I'm not nearly as precise as you are with measurements-- and never use step wedges-- and have not used the PDN system-- so you can take my wholly intuitive approach for what it's worth-- but I do give my yellow layer a couple of minutes longer than the blue or magenta.  I view the yellow layer as a highlight-- or just to give magenta a slightly different hue, so I don't mostly view yellow as it's own distinct color. (Maybe I have no images with just plain yellow in them. ??)   I've used yellow sometimes where I think it's completely washed off and hasn't added one thing, and then I'll add the magenta layer-- and when all the layers are there-- I see that what initially seemed like a very faint addition of yellow really has made a difference.  So I often think it *looks* like not much yellow has remained, but-- in fact-- (in my experience), it actually has added more than I first thought.  I always use quinacridone gold for the yellow.  For me, the yellow was yet another pigment where I tried several, and I just didn't like the way they worked, and the quinacridone gold seems, to me, to be the perfect color choice, and it performs perfectly.

Hope that helps.  I am 100% sure that others will offer additional and more precise suggestions. ;)

Diana


On Sep 26, 2012, at 1:23 PM, Johnny Brian wrote:

> Recently I've started the calibration process for 3 color gum printing with precision digital negatives, and encountered an issue I need advice about. I have been using PDN to make monochrome gum prints for a year or so, and had established 5 min 40 sec as a printing time with an Arista UV box. For the 3 color, I've used M Graham Azo Yellow, Phthalocyanine Blue, and Quinacridone Rose pigments 1/4 gm with 3ml gum solution and 3ml 10% potassium dichromate printed on Arches Platine sized with gluteradehyde hardened gelatin. I printed some small 21 step wedges and noticed that it would seem that the printing times should be different for each color. This didn't surprise me as I would assume that the pigment itself absorbs some of the UV light, reducing the amount of UV to react with the dichromate. To see the wedges more clearly, I decided to print 4x5 step wedges. For the PDN "standard" printing time, rose pigment was 4 min, cyan was 8 min but the yellow does not have merged ste
> ps outside of the pictorico film even with a 11 m 20 sec exposure. I printed with yellow at 5m 40sec, 8 min and 11m 20sec, and they actually look about the same - the longer print times are a bit darker, but the steps 1-2-3-etc inside and outside of the film are visually different - and different when measured with an densitometer. Maybe I need to increase the exposure more, but 11m 20sec seemed like a long exposure time. SO - 
> 1. Is it expected to have such wide exposure times with the 3 colors?
> 2. Should I try and increase the yellow exposure time even more? It seems like the steps outside the film should have merged already and I'm not sure increasing the exposure will make much difference. 
> 3. Unrelated to the above, but I've noticed that the blue (cyan) really tends to stain, even with the sizing (not really usable with out sizing the paper). The sizing also significantly changes the color of the blue. Anyone have a better suggestion for a blue pigment that doesn't stain as much?
> 
> Maybe this question is better for the PDN list, but I thought I would start here. 
> 
> Thanks,
> Johnny Brian
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