Gum Bichromate problem: no midtones, too contrasty

Fulvio · Mar 8, 2008

Hi,

I have posted more than one time my experiences with gum bichromate printing... Last month I had some partial success. I don't know why suddenly I'm not making any progress. I'm keeping notes of everything I do and I don't know what happened.

The biggest problem I have is that the tonal range of my prints is extremely compressed. The tones jump from black to white in a very few steps. No matter if I adjust exposure. And even with digital negatives there's no change (I use Mark Nelson's system). It's black and white. Almost no greytones.

This happens with most colors, but it's especially noticeable with darker ones (lump black, mixtures of burnt sienna and blue, etc.). With lighter colors occasional flaking occurs sometimes. Natural earth pigments give me less evident problems.

I use MaimeriBlu pigments. I live in Italy and these are easy to find. They're the top line of Maimeri watercolors. About 5 dollars for a 15ml tube.

I use winsor & newton gum. It's expensive, but if I try to mix my own gum acacia (~30% in distilled water) I always experience problems (flaking most of the time).

I use potassium dichromate. Mine saturates at about 10-11%. I make a 12% solution to be sure it's saturated (there's a little bit of precipitate in the bottom of the bottle). I store the solution in a dark glass bottle. Lowering the concentration to 6% doesn't solve the problem.

I mix the gum and the pigment on the spot. I use a 1:1 gum:sensitizer ratio. I have tried 1:2 and 2:1, but the problems won't go away. I found that 0.50-0.75 g of pigment every 3 ml of gum and 3 ml of sensitizer (that is 0.50-0.75 grams every 6 ml of gum+sensitizer solution) give enough color density and dont' stain the paper. Above 1.0g I start getting stains or flaking.

I coat my paper with a hake brush. One quick coat, then I use a second clean brush to help me even the coating. I have tried sizing the paper. The problems persist with sized and unsized papers. I tried sizing the paper with food gelatin hardened by alum or by coating the paper with gum arabic and potassium dichromate (without pigment), exposing and washing. The only advantage by doing this was to get sometimes finer details due to a smoother surface.

My goal is to be able to make a decent print with a single coat and a good print with a wider tonal range with three coats or more. But I'm far from getting there...

nze · Mar 9, 2008

Everything look good for but the coating may be a little better.
For a good brush coating of gum, I suggest to start by a quick coat as you wrote and then a long coat with a clean brush , keep on coating till the gum is still wet and do not resist to much. When you coat after each direction wash you brush again with a dry towel. For this part of the coating you a very soft brush this will help you to coat till the gu m is very thin on the paper.

Your problem may come from:
- too contrasty negative but you have good digitalcalibrated neg
- too contarasty sensitizer but yours look quite soft
- too heavy coating , I explain the solution above
- too short exposure
- too hot or acid clearing water.

When you put the print in the water bath did you see the image in negative??

best

dmax · Mar 9, 2008

Fulvio,
I've seen this sort of problem from some of the digitally-produced negatives used by some of my students. I do not work digital myself, so I certainly am not by any means entirely familiar with the process. One of the things we stumbled upon in trying to sort the problem out is that not all acetate sheets used for producing digital negatives behave the same way, nor do the dyes/inks. Some acetate sheets may block (or at least impede) the UV light you need to harden the gum emulsion. The same comment may apply to the specific type of ink/dyes you use to print out the digital negative.

A quick way to test whether it is your negative or your procedure that needs further examination: Shoot a regular negative and try to print it, using your normal protocol for gum dichromate mix, coating, exposure, and processing. This presumes you have a large format camera to work with. If not, shoot a few frames with a 35mm of a plain brightly lit surface like a wall. Begin with two blank frames, and then proceed with two frames at 3 stops less than what your meter indicates, then two frames at 2 stops, then one stop, and so forth until you have a short roll that gives you a full range of densities up to the maximum highlight density you normally work with. You can vary the number of frames per exposure depending on the size of your proofing frame to fit the negative strips. Process the film, then contact print using your gum procedure. If you get a full range of densities (or at least a decent spread from shadow values, midtones, and highlights) then your initial problem lies with your digital negative.

Katharine Thayer · Mar 9, 2008

Are people looking at something? Christian's answer, that it looks good but the coating might be better, and that the sensitizer looks "soft" gave me to think that he's looking at something, but I don't see anything to look at. Am I missing a link or an attachment with the post?

Going just on the information given, this looks to me a classic illustration of the age-old tradeoff you get with gum, that has little to do with negatives and everything to do with gum itself: the more pigment you use, the higher contrast (fewer steps) the print. The pigment mix you'd use to give you the absolute darkest value for a particular print will give you just a few steps; a pigment mix that will give a wider range of tones has to be less pigmented, and by definition won't give you the darkest value possible with the pigment. if you want the darkest value possible you need to fill in the shadows with a second printing with a short exposure with a heavier, high-contrast mix. As I always say, in one gum printing you can have either drama or subtlety, but not both. (The bleach-development method some have been experimenting with -- see alt-photo list archives-- seems to promise an exception to this rule, except that I can't make it work for me).

Compounding the high contrast inherent in the pigment mix is the high-contrast sensitizer being used. If you want more tones, I'd recommend backing off on the pigment and using a lower contrast dichromate mix. Here's an example of a one coat gum (this is a digital negative, by the way; it was one of my first prints with a digital negative and I didn't have the blocking color or the curve right yet, but I trust you can get the idea even though the negative isn't perfect) to illustrate the point. This is ivory black, the weakest (and warmest) black pigment, and not a particularly heavy mix of it, mixed 1:1 with saturated ammonium dichromate.

http://www.pacifier.com/~kthayer/html/kids.html
Katharine

Fulvio · Mar 9, 2008

I'll post later some scans of my recent prints, both from silver gelatin negatives and digital negatives

I tried reducing the pigment further to 0.10g per 6 ml of gum+sensitizer solution. I've been using carbon black... The result is a very low contrast image with ugly midtones, blocked shadows, blotchy highlights. If I try to reduce the dichromate or increase pigment, the image gets more contrasty, but with no detail in shadows, no detail in hightlights, no midtones, almost just black and white only.

My stouffer step wedge indicates an optimal exposure of 3'30". I use a self built UV box for exposure (400w).
With regular negatives I get too contrasty images... With calibrated digital negatives I get a lot of mess, as explained above.

A funny thing is that if I change the pigment, 0.75g of burnt sienna for example per 6 ml of gum+sensitizer, I need to increase the exposure up to 15-20 minutes otherwise I won't get the same results and the image will be really underexposed (still contrasty, but this time with blocked highlights and no shadows, just blacks in the deepest areas). Even with the stouffer step wedge, it needs to be exposed for 15-20 minutes to get the same steps as with the lamp black in 3 minutes. Why is that so?

When the print is put into water I always have to remove extra pigment with a brush. Even after more than one hour, almost two hours under running water, the image doesn't develop. If I gently brush away the excess pigment inside unhardened gelatin, the image reveals (but it's like described above).

Your website is a good source of informations for me Katharine... But I'm not getting anywhere close to your beautiful prints...

I'll post some pic later.

sdivot · Mar 9, 2008

Fulvio,
How do your tonal palettes/calibrations look from the PDN system? Obviously, if you can't get a good negative to use, you'll never get a good print.
I found it almost impossible to get seperation between the first two steps on the 31 step wedge with gum. I settled on 100 units of exposure with my Nu-arc unit, and based everything on that. I've read that others have done it this way as well.
I would suggest you get Chrisitna Anderson's book on alt processes. There's an extensive section on gum printing in the book.
I also suggest you standardize as much of the process as possible. Take out the variables. Mix your 15ml tube of pigment with 50ml of gum and use it as a stock. I actually use 1 part gum/pigment stock, 1 part saturated am. dichromate, 1 part straight gum, and 1 part water. I use a roller to apply a thin layer of gum, rolling with less and less pressure until smooth.
Use distilled water in your bath just in case, and stick with a set time in the bath with a set temperature. I use 30 minutes.
Forget about getting a good print with a negative. Get your PDN tonal palettes right first.
I'm doing 3 color gum prints right now, and they are looking pretty good. I use the PDN system and follw Chris Andersons guidelines.
Botton line: Standardize, eliminate variables. It's a finicky process, so make your life easier.
Hope this helps a little,
Steve

Fulvio · Mar 9, 2008

here are some first attachments

0.10g lamp black in 3 ml gum + 3 ml sensitizer (saturaded potassium dichromate)

the stepwedge scan shows print result after 3 minutes exposure

the file gum01.jpg shows the print of a silver gelatin 4x5" negative with same exposure

the file gum02.jpg shows the print of the previous negative with 2 minutes exposure (but I have used 4 ml gum + 2 ml sensitizer for this print, thus reducing the ratio to 2:1)

the scans look MUCH BETTER than real life...

Fulvio · Mar 9, 2008

yes I'm using Mark Nelson's PDN system

I print my digital negatives with an Epson R2400 printer and have no problems with any other kind of alternative process

in the attachments you will find the tone charts with and without curve applied

same exposure time, 3' as indicated by the step wedge before, lamp black pigment - but if I try to print on a different pigment, a natural earth for example, I need to raise exposure up to 15-20' otherwise most of the print will be washed out in the developing stage

again, these scans look MUCH BETTER than actual prints

surprisingly the scanner is picking up more details than naked eye (usually is the opposite)

Fulvio · Mar 9, 2008

this is what I'm talking about, if I switch from lamp black to earth pigment...

burnt sienna instead of lamp black, same gum-sensitizer mixture,
same exposure (3'), same curve (pdn), but this is the result

if I raise exposure up to 20' then it's correct, and I get a similar image to that posted before for the lamp black (but with some problems in the highlights, flat contrast, etc.)

sdivot · Mar 9, 2008

Fulvio,
I suppose some colors may be more opaque than others, requiring more exposure time. I haven't experienced such a difference between colors.
You may want to try a different brand of pigment. I use winsor newton.
I would also think about your coating method. Make sure you have a very thin coat, and don't brush develop your prints unless you're planning to do that as a regular part of your workflow. Such a thin coat may make several coats necessary, but they will be smoother.
How is the quality of your water? Can you use distilled?
Good luck,
Steve

Katharine Thayer · Mar 9, 2008

Fulvio, thanks for pictures, but now I'm confused. The original question, which I answered, was about a high-contrast image where the dominant tones are black and white without greys in between. But the scans are of very low-contrast images and charts where there's pretty much one mid-grey tone without much range either direction. I do see that in the original question, you were talking about .50-.75 g pigment in 3 ml gum, whereas for the scanned images the pigment load is much less, .10 g in 3 ml gum, which makes sense given the images, but.... as I said, I'm no longer sure what the question is. If it's why are these images so low-contrast, so lacking in tonal range? The answer is: not enough pigment.
Katharine

Fulvio · Mar 13, 2008

sorry for the confusion... actually you helped me a lot, especially Katharine with her website full of informations

I had to adjust carefully the quantity and exposure for each different pigment, that's the key of the process

I have my first successful print, it took me several nights to complete (see the attachment)

it's 5 color (mars red, burnt sienna, raw umber, burnt umber... and a final layer of burnt umber + cobalt blue instead of black)

I gave up the idea of using carbon/lamp black... it leaves too many spots in the paper and the effect is unpredictable... Ivory black is too weak, in fact looks like a gray.

I still had some problems

I did not size my papers, though (I'm using Fabriano 5 for now). With earth pigments stains and spots are not an issue. But there were hundreds of tiny dark spots in the white areas (britghtest highlights) when I coated the last color (the umber/blue mixture to replace black). I was able to fix it with some white chalk.

Do you think I can overcome this issue by sizing papers? I don't want to use formaldehyde... I was thinking about a 1% gelatin solution (food gelatin or fish glue) and some 5% potassium alum as hardener... do you believe it will work?

thank you

smieglitz · Mar 13, 2008

Alum doesn't seem to harden as well as some other agents. Try it though. If it doesn't work for you, consider doing an initial layer of unpigmented sensitized gum as a hard underlayer for your image. Coat the paper with unpigmented gum and dichromate and give an exposure sufficient to harden the layer. Any color cast from the dichromate can be removed later with a 5% sodium or potassium metabisulfite treatment.

Other hardening agents (glyoxal, glutaraldehyde [sp?], etc., are available and have been discussed at length in the alternative process mailing list archives.

You might also try different sizing agents. I think canvas hide glue sizing is a bit tougher than ossein which seems harder than food gelatins. No hard data (pardon the pun) to back that claim, but it seems so by casual observation. I've also used laundry spray starch in between gum layers with some success in the past.

Joe

Fulvio · Mar 13, 2008

how about gesso? does it need to be hardened when dry?

smieglitz · Mar 13, 2008

Gesso can be used though it is not a personal reference. It is very rough unless diluted considerably and it destroys the surface quality of the paper IMO. (The paper looks painted to me with gesso rather than retaining the look of a gelatin-sized sheet. YMMV.) I also think it becomes more prone to flaking, but I've never liked the gessoed surface enough to keep at it and nail the relationships down.

If experimenting, you might begin with a dilution of 1:4 or higher to gage practicality. No need to harden the gessoed surface.

Joe

Tomf2468 · Mar 13, 2008

With papers that handle gum/paint well (such as you are using) I'm a big fan of brush sizing with gelatin and glyoxal. I mix a small amount of the hardener into the gelatin, making only as much as I will using in a few hours. This means I don't have big tubs of smelly/dangerous hardeners in my darkroom. Remember, it is the portion that makes the poison!

My usual routine is to room temperature soak the paper for 30 minutes and let it completely dry (to pre shrink). Then I brush the gelatin sizing onto the image size of the paper.

For every 100ml of sizing:
Start with 80ml of room temp water
Add 2 grams of gelatin (I like 250 bloom hard gelatin, but Knox will work)
Let sit (swell) for about 5 minutes

Add 1ml of 40% glyoxal (see how little of the dangerous stuff is used! I assume you could substitute glut or formalin here, but glut is hard to buy and formalin stinks too much))
Add 5ml of cheap Vodka (Optional, helps with spreading and eliminating bubbles)
Add enough water to make a total of 100ml
Stir well

Heat in a double boiler until the gelatin is between 120 and 130 degrees F (my double boiler is simply one beaker with the gelatin sitting in a much larger beaker with water)

Paint the gelatin onto the image side (only) of the paper. Use lots, get the paper as wet as it can be without being runny or drippy.

Let dry for at least 4 hours, to allow all glyoxal to "out-gas".

Again, this method is for gum friendly papers. It uses a weak gelatin with very little hardener and only coats one side of the paper. Those are all good things, assuming you have a friendly paper. You would get a lot of staining using this method and BFK paper!

Tom

donbga · Mar 14, 2008

Tomf2468 said:
Again, this method is for gum friendly papers. It uses a weak gelatin with very little hardener and only coats one side of the paper. Those are all good things, assuming you have a friendly paper. You would get a lot of staining using this method and BFK paper!

Tom

I use Rives BFK and normally have no problems with staining. It's one of my favorite gum papers.

Instead of using glyoxal, I use gluteraldehyde <sp?> as the hardener and it works much better than glyoxal. The hardened gelatin surface is smooth and soft and takes multiple coats very nicely. Same for gum overs also.

Glut must be handled and used with care though. If you use it, have plenty of proper ventilation and wear eye protection as it can easily damage mucous membranes and soft tissues such as the eyes.

http://en.wikipedia.org/wiki/Glutaraldehyde

I use 6 ml per liter of a 2.5% solution of glut per liter of a 3% gelatin solution. I treat parent sized sheets rather than smaller pieces to minimize the chore of sizing.

Tomf2468 · Mar 14, 2008

Hello Don,
I wasn't intending to insult your favorite paper! There are always 12 good ways of doing anything in the art world. I was just pointing out that the method I outlined (using less gelatin and a less toxic harder) was great for the paper that Fulvio used, but wasn't appropriate for softer papers (such as BFK).

I've been using mostly Aristico lately. As long as you don't shrink Aristico with 120 degree water, it really doesn't need much size! However, some other papers are collecting in the darkroom calling my name...... So I may need a stronger size soon and I no longer have a local source for my old hardener, formaldehyde. I miss Tri-Ess, it was just down the freeway from my home. Are you brush sizing or dunking the BFK paper? Where do you buy the glut?

Tom

donbga · Mar 14, 2008

Tomf2468 said:
Hello Don,
I wasn't intending to insult your favorite paper! There are always 12 good ways of doing anything in the art world. I was just pointing out that the method I outlined (using less gelatin and a less toxic harder) was great for the paper that Fulvio used, but wasn't appropriate for softer papers (such as BFK).

I've been using mostly Aristico lately. As long as you don't shrink Aristico with 120 degree water, it really doesn't need much size! However, some other papers are collecting in the darkroom calling my name...... So I may need a stronger size soon and I no longer have a local source for my old hardener, formaldehyde. I miss Tri-Ess, it was just down the freeway from my home. Are you brush sizing or dunking the BFK paper? Where do you buy the glut?

Tom

Hi Tom,

Sorry if I sounded insulted, that was not my intent. I also use FAEW and size that as well. I just wanted to point out that BFK isn't a hostile paper for me.

I only size with a 6 inch foam brush. Normally I'll pre-shrink batch of 10 parent sized sheets and then have a marathon sizing session in my garage (during warm weather) and size a 100 sheets, 15 sheets at a time. The sizing dries quickly but I let them hang for 4-5 hours before they are removed and stored. I place the stack in a flat file drawer with other reams of paper stacked on top so they will flatten after a few days. Boring work for sure but it seems more efficient to do sizing this way.

You can get glut from Photographers Formulary or at least you used to be able to get it there. It's been a long time since I've purchased any.

I actually purchased a liter of Formalin at local pharmacy. I just happend to see the bottle sitting on their shelf one day and asked them if I could buy it. They were happy to sell it to me since it had been ordered erroneously and could not be returned. Perhaps you could get your druggist to order some for it. I still haven't used any but I probably will compare it to glut this summer.

Glut is far superior for sizing IMO than glyoxal but it does need to be treated with respect. In my gum workshops I pre-size the paper in advance, but I do do a sizing demo with a cheap piece of paper with no hardener in the gelatin. I find that it takes about 35 ml of 3% gelatin to size a 22x30 inch sheet of paper, YMMV.

Lyn Arnold · Mar 14, 2008

Don, how much formalin would you use for 100ml sizing?
Thanks in advance, Lyn Arnold

donbga · Mar 14, 2008

Lyn Arnold said:
Don, how much formalin would you use for 100ml sizing?
Thanks in advance, Lyn Arnold

2 ml of Formalin (37%) per 100 ml 3% gelatin. The 2 ml of Formalin is part of the final 10ml volume of gelatin size.

donbga · Mar 14, 2008

Lyn Arnold said:
Don, how much formalin would you use for 100ml sizing?
Thanks in advance, Lyn Arnold

Use Formalin with caution too. It has the potential to damage your eyes and other mucous tissues. It is a know carcenagen.

Katharine Thayer · Mar 15, 2008

Fulvio said:
I had to adjust carefully the quantity and exposure for each different pigment, that's the key of the process

Bingo.

Autumn Rainbolt · Feb 5, 2019

I would start with looking in your potassium dichromate. Your concentration of the potassium dichromate is probably too high, this causes the printing speed to increase. You can try to reduce the exposure time of your print, or you can reduce the saturation to about 5-6% and continue with the same exposure times you are currently doing. Since your concentration is probably too high the solution oxidizes more quickly. If you are not careful this can reduce the contrast in your image. Which is why you are having a difficulties in getting those greyish tones. Flaking and a loss of contrast strictly come from your image being exposed. Gum bichromate printing process involves a chemical reaction between the gum arabic and potassium dichromate, light activates the chemical reaction causing the exposed parts to the light to oxidize. The pigment you use does not affect the chemical reaction at all. My gum solution is typically 70g/100 mL water, and my potassium dichromate solution 11.7g/100g solution. I use a large format black and white transparency that is around 4 inches by 6 inches.

Autumn Rainbolt · Feb 5, 2019

Fulvio said:
how about gesso? does it need to be hardened when dry?

Do not use gesso when trying to create a gum bichromate print. Gesso is used as the first coat for an oil painting in order to prevent flaking, usually on a canvas. For your gum bichromate print I would try coating a thin layer of water, applied with a sponge paint brush, before painting on your solution.

Gum Bichromate problem: no midtones, too contrasty

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