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

Wed Sep 26 21:51:28 GMT 2012

Johnny,

I have to agree with Diana on the cyan choice. Prussian blue is low staining (I use Daniel Smith brand for all my gum printing). For a tricolor gum the first cyan layer (it is necessary to print cyan first for lightbox registartion) should be much lighter then you would think. Actually my practice is to almost always to start with a light cyan    layer and then come back with a 4th cyan layer to deepen the shadows. While phtalocyanine pigments are wonderfully primary cyan hue, they are also the most staining.
Try indanthrone as another blue non-staining pirment that prints well in gum. 

If you are using nickel azo yellow (it was not clear from your description), it is much stronger then corresponding blue and cyan tubes and I found I had to cut the concentration in half. I print my negative separations with the same pigment mix (on my 3800), but I adjust my exposures, which are typically 1-2 minutes.  Using the same ink setting for all the separations certailny makes thigs easier and I never found it necessary to alter my practice. Gum printing is so variable that "overtuning' gets swamped with other parametrs that are typically much less controlled 9like development time temperature agitation, etc). Perhaps a better way of controlling some variables is to make standard gum solution of your colour pigments. It allows for a good pigment concentration control.
I woould not worry too much about yellow tests. Perhaps you are exposing them so much as to be getting dichromate stain, rather then yellow pigment layer. It is almost impossible to see the yellow on white paper and as Diana suggested even if you do not think you have any you actually have some. Try to use cyan negative for your yellow test. perhaps you have done something wrong with the yellow separation.

Try printing test prints rich in shades of green to learn about yellow-cyan interactions. Print rich in grren shades is also a great way to test your different cyan pigments.

Have fun at it

Marek

> From: dlhbloomfield at gmail.com
> Date: Wed, 26 Sep 2012 14:10:22 -0400
> To: alt-photo-process-list at lists.altphotolist.org
> Subject: [alt-photo] Re: 3 color gum and PDN calibration?
> 
> 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 anot
> her 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 s
> te
> > 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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