Color Gum Bichromate Printing - color management?

[jag2x]

Hi all,

I havent as yet done any basic gum printing. Though I would like to understand all the processes fully before I begin.
At the moment I print B&W prints using the ilford multigrade darkroom paper, using imagesetter negatives. I followed the Yule/Neilson Density table supplied by Huntington Witherill (www.huntingtonwitherill.com). Which has been very valuable to me in trying to figure out with a densitometer, what the corresponding density values are from my print to the percent values in photoshop "K Values". E.g my Ilford paper Dmax is 2.04, Dmin 0.00, and the 50% K Value reading from the chart corresponds to 0.66 in density. Once I figure out all the values I make the curve and apply it to the image in Photoshop and get the resulting imagesetter negative.

Alright that I understand, now the next phase is trying to print color seperation negatives for color gum bichromate printing.
From what I've been reading I can produce these negatives easily with the cmyk channels, producing 4 B&W negatives.
Say I want to know what my densities are for K channel is going to be, so I use a black watercolor paint and use a step wedge to print. Now I presume I use the same method as I did before. Using my densitometer and figuring out what my DMAX and DMIN is for the paper(following the Yule.Nelson Density Table). Then creating the curve for that K channel to get a good tonality from 0 to 100% "K Value".
Now the questions are:
Once I get this curve do I use this curve on all the other channels? C, M , Y?

Would exposure time be different or the same for the K channel print if I printed C,M or Y?
Do the watercolors I use for the other channels have to be taken into consideration?

Excuse my ignorance but I know very little about color targeting/profiling, is there a way to use a method to match a base watercolor cyan (Thalo blue) (or any other pigments that I use for the other chanells)print pigment to correpond to actual value in Photoshop? I understand scanning it would be one method, would a color densitometer help in this instance or those Gretag Macbeth type systems work here? Though I rather not scan and match by eye, I would like to use a denistomter if possible?

So the main purpose is to get the actual color image on the computer to look almost like the final print.

Am I way off target, are these valid questions to ask? What other questions should I be asking when it comes to color printing?

I understand printing color Gum Bichromate is riddled with a million factors, but I just want to get a better picture (pun intended) of all the processes and being able to control each step.
Ta
Jacek

 

[Doyle Thomas]

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Once I get this curve do I use this curve on all the other channels? C, M , Y?
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I as yet have little little experience but I have attempted some tri-color Gum Dichomate printing. I understand what you want to do, ie fixed exposure and development time per layer = correct color balance. It won't be that easy if my experince is any indication.
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Would exposure time be different or the same for the K channel print if I printed C,M or Y?
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depends on the pigments used, see below.
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Do the watercolors I use for the other channels have to be taken into consideration?
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Yes, there are many factors including the pigment density and the pigments opacity to UV light.

As you said, Gum Bichromate (dichromate) is riddled with a million factors. I have been looking out for a good class/workshop for about a year now. Let me know if you hear about one.

I will look into the Yule/Neilson Density table you mentioned.

Doyle

 

[timeUnit]

Gum printing is very very different from silver gelatin printing. It will take years of practice to be able to produce coats that are consistent in Exposure Scale, Density, Hue, Saturation and Opacity. As each coat you make will be different, there is no use trying to create negs with carefully compensated/linearised curves (IMO).

I would suggest you try to match the ES of each of your gum pigment mixes with the DR of your neg. Maybe you'll make general compensations in the curve(s) to match/separate certain values better, but this is probably something you'll do later on, when you've gotten the hang of things.

From there on, it's more of an improvisation. "Maybe this print would benefit from an extra cyan layer." "Maybe I will choose a lower contrast gum/dichromate mix for the magenta layer in this print." Try and fail, try and succeed.

Getting perfect color balance with gum prints is achievable, but very difficult. IMO the beauty of gum printing is in the unlimited possibilities of interpreting an image into a print. Making perfect color balanced prints is just not it's strength -- it is the exquisite cross between photography and painting, the way one works with the pigments while wet, etc. And of course how the end result is on a beautiful art paper, and will stand unfaded for hundreds of years.

 

[Katharine Thayer]

Gum printing is very very different from silver gelatin printing.

Amen, brother.
kt

 

[donbga]

It will take years of practice to be able to produce coats that are consistent in Exposure Scale, Density, Hue, Saturation and Opacity. As each coat you make will be different, there is no use trying to create negs with carefully compensated/linearised curves (IMO).

TU,

Sorry but I have to disagree with you. You can become profficient at gum printing in a few weeks. Also digital negatives can be made that work predictably <sp?>.

I would suggest you try to match the ES of each of your gum pigment mixes with the DR of your neg.

This may not be possible depending on the DR of the negative.

Regards,

Don Bryant

 

[Katharine Thayer]

TU,

Sorry but I have to disagree with you. You can become profficient at gum printing in a few weeks. Also digital negatives can be made that work predictably <sp?>.

I agree with Don that it doesn't take years to become proficient and consistent with gum printing. Look how fast Denise is picking it up, for example.

But I also agree with doyle and henning in their responses to the OP, when they say that precise color matching in full color printing isn't as simple as he was hoping to make it; it's at least as much a matter of understanding the pigments you're using and how they interact with each other (see the discussion about tricolor gumover in the silver gelatin thread for an example) and balancing their proportions correctly, as it is about dialing in curves for each of the individual colors.

What I was agreeing with in my earlier response to Henning's post was the opening sentence specifically: gum printing is very different from silver printing; I responded to that before I even read the rest of the post, because it resonated so plangently with my thoughts from the other thread where I argued that it doesn't make sense to lump gum in with other alternative processes, such as when making generalizations about matching print tones to the tones on the monitor.
kt

 

[timeUnit]

OK, I'll back down a bit from "years of practice" statement. I meant that it is quite difficult to create two gum prints that are indistinguishable from each other, ie with a very high degree of consistency in mixing, coating and exposure. At least that's my own impression after doing the process for a little while (and my teacher seems to agree after 20 years of experience). And, to me, that's the beauty of it.

 

[timeUnit]

This may not be possible depending on the DR of the negative.

Regards,

Don Bryant

The gum process seems to need a DR of around 1,2, or so I've heard. Unfortunately I don't have a densitometer and have no means or checking my negs that way. It's trial and error for me.

Anyway, most digineg-processes should be able to produce a neg of that density, right? At least my Epson 1290 has no problems with it.

But then again, the ES of gum bichromate is very short, and with a low Dmax compared to other alt. processes. So one cannot always expect to get all tones on a full neg onto paper in one layer. One might need an extra high contrast layer for that punch.

In my limited experience, anyway.

 

[dwross2]

Hi All:

I've been looking in on this thread and the "curving out emulsion" one with delighted interest. Every time someone made a comment I went, 'Yeah, me too'. I think it was Katherine who made the comparison of the blind men and the elephant to gum. I've decided that is spot on.

I want to believe that it is possible to get the gum process down to where one could reliably make near identical copies, but I'm sure not there. So many variables! Light output, heat, humidity, what looks like a degree of self-masking dependent on how thick you get a coating... well, you gum veterans know far better than I. It's fun, though. I'm convinced there's a lot of potential in crafting the color separation negatives. Lot of work, too.

Katherine: I think I have basically worked out a (as in one) color set that works. I have deliberately printed heavy so that I can see the combinations in three coats. Blue: one to one Phtalo blue and Carb.Violet DS water soluble inks, Yellow: one to one Hansa Yellow and Lemon yellow DS watercolors, and Red: one to one DS Rhodonite Genuine and Quinacridone Red. I like the results (although I'm printing too strong for my personal taste) but I'm going to try to get away from the inks. Yuch! smelly nuisance stuff.

I going to try to post attachments here. Let's see if it works.

d

 

[dwross2]

Well, I don't think that worked. Try, try, and try again. Sheesh.

Ok, it's to the Gallery.

 

[Katharine Thayer]

Hi All:

I've been looking in on this thread and the "curving out emulsion" one with delighted interest. Every time someone made a comment I went, 'Yeah, me too'. I think it was Katherine who made the comparison of the blind men and the elephant to gum. I've decided that is spot on.

Actually, I was using the analogy of the blind men and the elephant specifically in the context of the tonal inversion discussion; I truly don't think we collectively, or any of us individually, yet understand the cause(s) of that particular phenomenon. I've come to believe, as I said in that thread, that it's probably a very complex interaction between several variables that we may never completely understand. But those remarks shouldn't be overinterpreted to mean that I think the same feeling-in-the-dark, no-one-seeing-the-whole-picture analogy extends to all of gum printing, or that I think gum printing is unfathomable or unpredictable; nothing could be farther from the truth.

As for the subject of this thread, I don't think it's awfully difficult to make predictable or repeatable tricolor gum prints; all you have to do is find a pigment combination and gum/pigment proportions that provide the desired color palette and color balance, and work out a routine that produces the desired result in the final print; once you've settled on that, all you have to do is use the same mixes and follow the same steps over and over.

As I've said elsewhere, but maybe not here, I stopped making tricolor gums in 1999 because I got bored with the rote tedium of it; I told someone I felt like I was working on an assembly line; besides I wanted to print in monochrome, not in color, and to explore some of the other effects that gum was capable of. It's only been in the last couple of years that I've started doing some tricolor gums again and enjoying it, but I don't see myself ever again going into full production mode with tricolor gum.

If your pigments and proportions are in good balance to start with, then it's possible that curves could add an extra level of tonal perfection to the tricolor print. I have yet to test that proposition, although it's on my list of things to do. But if they aren't, no curves are ever going to make them so.

I've had considerable private correspondences with people starting with tricolor gum, some of whom assume as the OP here seems to assume, that it's simply a matter of properly calibrating the individual layers, and are surprised to find this approach doesn't produce perfectly balanced color prints. With tricolor gum, in my experience, it's the interaction between the layers that determines the final outcome much more than the calibration of the individual layers, and I'm not sure I even want to think about what would be involved in trying to calibrate three layers as a group, rather than individually. But the point is that it's not necessary to go that route; practice will get you there much faster than calibration ever could.

As I've said in another thread, I think gumovers and straight gum prints are rather different, and one probably shouldn't try to generalize from one to the other.
Katharine

 

[Katharine Thayer]

The gum process seems to need a DR of around 1,2, or so I've heard. <snip>

But then again, the ES of gum bichromate is very short, and with a low Dmax compared to other alt. processes. So one cannot always expect to get all tones on a full neg onto paper in one layer. One might need an extra high contrast layer for that punch.

Henning, I think this is an example of the difficulty we encounter when we try to translate process calibrations appropriate for metal processes to gum printing, which as you rightly said earlier is very different from silver.

The ES, meaning the number of steps printed on a 21 or 31-step tablet, can be fairly long for gum, actually; I've heard reports of people printing 21 steps with a lightly-pigmented mix (although I've always suspected that with such a mix the steps must be so close together tonally that it would be hard to distinguish them). As a general rule, the more steps a mix will print, the lighter the mix is and the lighter the DMax; the fewer steps a mix will print, the darker the mix is and the darker the DMax (assuming you're talking about one particular pigment; it gets more complicated as you compare pigments to each other). At any rate there's always a tradeoff that you have to consider with any mix, and there's no mix that will cover the entire range from the darkest DMax gum is capable of (1.8-2.00) to the lightest DMin gum is capable of (a whisper below white) which is why it's necessary, as you rightly say, to print more than one layer if you want a longer tonal range in the print than it's possible to print with one mix. Hope that makes sense,
Katharine

 

[dwross2]

Katharine:

My apologies for misinterpreting your feelings about the inherent repeatability of gum. I'm still very much groping around and about the elephant.

From my experience so far, I would add the color separation negatives to the equation. If part of the work flow for a particular print involves a lot of selective pigment removal, I think I would have a hard time getting nearly identical subsequent results. That's not a problem with one-offs (might even be considered an advantage) but could be a nuisance if one were trying to make editions.

My current set is as identical as possible to my last set with the exception that I have tweeked the separation negs to reflect the selective pigment removal I did manually before. (Nothing elaborate, just burning and dodging. My PS skills are 'unsophisticated' to say the least.) I still have the last (red) layer left, and I won't get to that before the weekend, but on the first four layers, I've hardly touched the prints post-development. I'm not saying that's necessarily an ideal. I like playing with my prints, but it is encouraging to know that a fair amount of repeatability is possible. Someday, I hope to get to your level of confidence and skill. A great goal!

d

 

[Katharine Thayer]

From my experience so far, I would add the color separation negatives to the equation. If part of the work flow for a particular print involves a lot of selective pigment removal, I think I would have a hard time getting nearly identical subsequent results. That's not a problem with one-offs (might even be considered an advantage) but could be a nuisance if one were trying to make editions.

Interesting; it just shows how many different ways there are to get to a goal in gum printing. I didn't realize that you were removing pigment; since I've always still-developed, it wouldn't have occurred to me.

Certainly if you're removing pigment to achieve the desired results, then some adjustment to the separations (if the pigment concentrations are deemed to be in balance) would be in order; it would be almost impossible, as you say, to remove pigment in exactly the same manner every time to get repeatable results, and I admire your ingenuity in developing a way to deal with that. Curves would be another way to approach it, but whatever works, is the main thing.

On reflection I think that what I said earlier about curves wasn't exactly what I meant, but I can't at the immediate moment come up with a better way to say it, so I'll leave it there til I can. For the moment, I'll just repeat that whatever is necessary to get the desired result is what's necessary.

For example, back in the pre-photo-quality-inkjet-printer days, when I was printing separations on a laser printer from bitmap files, I needed a very extreme curve because of the nature of bitmaps. Now, I need a very minimal curve, or no curve at all. (For that matter, there's always a curve, it's just that sometimes it's just a diagonal line). At any rate, nothing I say about what is required in my case should be taken as a pronouncement about what others should require; first of all I don't think that way, and besides, what curve is required is very individual depending on printers, light source for printing, a lot of things. Whatever's necessary, is what's necessary.

As to whether still development without manipulation is an ideal for predictability in gum printing, certainly I would think so. As I said, I've never been one to touch the print even during development, much less post-development, so you'll get no argument from me on that count.

You'll be there a lot faster than I was; I printed gum pretty much full time for a year before I felt I had mastered it.
Katharine

 

[dwross2]

Hi Katherine:

What I knew about gum printing three months ago was from a seminar 25 years ago at Arizona State University, given by a person considered the definitive authority at the time (and now, I have absolutely no memory of his name). He still-developed in four trays (as I do) and then pulled out the print and very carefully removed unwanted pigment. I've seen this technique described in everything I've read, so I assumed it was a "time-honored" technique. Actually, I thought I saw something you wrote about the stream of water you used being a little too powerful so that you erased pigment you hadn't intended.

I'm very comfortable with the idea that a handmade print has a lot of hands-on. After all, a 'perfect' and perfectly repeatable photographic product is always available with the push of the "Print" button .

d

 

[Katharine Thayer]

Hi Katherine:

What I knew about gum printing three months ago was from a seminar 25 years ago at Arizona State University, given by a person considered the definitive authority at the time (and now, I have absolutely no memory of his name). He still-developed in four trays (as I do) and then pulled out the print and very carefully removed unwanted pigment. I've seen this technique described in everything I've read, so I assumed it was a "time-honored" technique.

I don't know if it's time-honored or not, but it's not anything I've ever done.

Actually, I thought I saw something you wrote about the stream of water you used being a little too powerful so that you erased pigment you hadn't intended.

Funny... that was in a discussion on APUG about PBk 11, where Demachy's techniques were brought into the discussion by someone else. Just for fun, I tried replicating Demachy's recommendation to make a really stiff pigment mix brushable by doubling the dichromate solution in the mix. I explained in that thread that I forgot to reduce the exposure to adjust for the doubled dichromate, and overexposed the thing so profoundly that blasting the hardened gum/pigment off was the only way to get it to develop at all. But that's not to say such blasting is part of my usual practice, by any means, in fact if memory serves me correctly, it's the only time I've ever done anything like it. But it did help me understand Demachy's method better.

I've got nothing against handwork, or forced development either, just saying it's not something I do in my own printing practice, although that experience with the Demachy experiment got me thinking about trying it some more. Whether I actually go that way for the bulk of my printing, is doubtful.
Katharine