Multilayer gum printing - adhesion

walter23 · Feb 26, 2010

I'm trying to figure out multi-layered gum printing, and the problem I'm having is that the second layer doesn't adhere. I may have not had enough dichromate in the sensitizer for my second layer (I mix very small amounts at a time (0.3 grams of potassium dichromate in 3-4ml water), and my scale has an error of +/-0.1 grams), but I wanted to see if there were other possible problems to consider.

WHen I printed my second layer it started to develop okay, but then lifted away from all the exposed areas in solid clumps... so it hardened alright (or at least, to some extent), but broke up and didn't adhere.

I do a sodium metabisulfite bath to clear dichromate stain; could that be impacting things if I didn't rinse enough? I'm not really sure what to consider here.

I hope I don't have to size, but from what I understand sizing is about keeping pigment from adhering too much / staining, so I don't think that's what's going on here.

Katharine Thayer · Feb 26, 2010

Walter, what are you printing on? In my experience/observation this is a problem that tends to arise when printing on hard surfaces (plastic, metal, or glass, for example) that have little tooth, or when a too-thick or too-heavy size is used on paper so that it fills up the tooth in the paper and doesn't leave enough for the gum to hang onto. It sounds from your comments like you're not sizing, so the second possibility shouldn't apply, and if you're using paper, the first shouldn't apply. Varying amounts of dichromate would affect the speed of the gum layer but if the gum is coming off in flakes rather than washing off as a liquid (meaning the layer isn't sufficiently exposed) then I don't think it's the dichromate that's at fault.

Another question: how heavy is your pigment mix? If too heavily pigmented, it can chunk off like that, but if it's that heavily pigmented, you would have trouble brushing it on the paper as well.

Metabisulfite should not be an issue here, at all.

Hope any of that is useful,
Katharine

walter23 · Feb 27, 2010

I'm printing on Fabriano artistico hot pressed; no extra sizing added.

Interesting you say that too much pigment can do that; I doubled up the pigment for the second layer thinking I could avoid colouring the highlights by having more pigment but a shorter exposure (was aiming for higher contrast). Also it brushed on with a bit of difficulty and I couldn't get a smooth coating, it seemed too wet / runny. (This was also a different watercolour that I noticed had both gum arabic & dextrin as the base, instead of just gum arabic, so maybe that's an additional problem).

The first layer was a very small amount of pigment and a long exposure (to try to get the highlights filled in without adding much density to the dark areas; low contrast)... there was quite a bit of hardened gum on the paper after this (so you could really see the texture of it while it was wet; pretty serious relief). I had this "brilliant" idea to try to do something similar to split grade printing on multigrade silver paper (a low contrast exposure for the highlights followed by a high contrast exposure to fill in the shadows).

Instead of doing these radical pigment concentration things maybe I should try just using a lighter pigment (like transparent yellow) for the highlight layer, then a dark pigment for the shadows?

BTW, I have referred to your site quite a bit while learning this process; you've done some really nice stuff. Thanks for offering your suggestions.

Katharine Thayer · Feb 27, 2010

Hmm, I don't think we're talking about the same thing with the pigment; wet/runny doesn't describe the kind of heavily pigmented mix I'm talking about. I was talking about a mix that's so heavily pigmented it's like tar, and the difficulty I was referring to would be akin to trying to spread tar on paper with a brush. If a mix is wet and runny, I would say it's not heavily pigmented, by definition. Do you use extra water in your mix, or just the water in the dichromate solution? BTW, I'm not sure I see the reason for mixing such tiny amounts of dichromate; that seems like a lot of trouble to me.

FYI: the same issue has been just recently been brought up on the alt-photo mailing list, someone having the same problem of third and later gum layers not adhering, same paper (Fabriano Artistico Extra-White) unsized.

I don't use that paper, don't like it, but when I did try ten sheets of it just to see what all the hoo-ha was about, I found it a very absorbent paper, very easy to coat (which may be why so many people like it) which disqualifies it from the category of hard/slick/nonabsorbent materials that I was referring to in my earlier post, that can sometimes have difficulty hanging onto subsequent layers.

Your thinking is good with the "split tone" idea; that's how generations of gum printers have printed both well-gradated highlights and dark shadows. Sorry it didn't work in this case. But there should be no problem with your method; I've done this routinely.

I'm afraid I don't have any good answers, since the usual answers to this question don't seem to apply. Just grasping at straws, I'd say try a longer exposure for the second coat and see if that helps. Good luck,
Katharine

walter23 · Feb 27, 2010

Thanks Katharine; appreciate the help.

For now I'll assume my first layer is okay and just try to sort out the second layer issue. I probably just made a bad batch of gum / sensitizer, it didn't seem to brush on right, and even a test print with just one layer of that batch didn't seem right to me (took a much longer exposure than normal).

Should find a brown bottle and mix up a bigger batch of sensitizer to keep it consistent and make proportions easier to control. Does the dissolved dichromate solution last any reasonable length of time?

Dan Williams · Feb 27, 2010

Katherine didn't toot her own horn. Click on the URL at the bottom of her reply and it will take you to her website where you will find a wealth of information on gum printing.

Dan

walter23 · Feb 27, 2010

Yeah, I have really enjoyed looking at her work and information... thanks for the reminder, lots of good information there.

PVia · Feb 27, 2010

AFAIK, the dichromate solution should last a long time esp in a brown bottle. I made my first bottle in May of 2009 and it's still perfect. Find a 100ml bottle and mix it up all at once. There's too much of a variable when mixing tiny amounts for one-time usage.

sdivot · Feb 27, 2010

The easiest thing to do is just mix up a saturated dichromate solution. Keep adding water until no more will dissolve, and you have a saturated solution. You can keep this in a big amber bottle and keep adding water until the dichromate will eventually all dissolve. At that point, add more dichromate until it's saturated again. This way your mix will always be consistent. I think it will last a very long time.
Just make sure you don't shake the bottle before measuring it out for your print, or else you will get dichromate crystals in your mix.
Steve
www.scdowellphoto.com

walter23 · Feb 28, 2010

sdivot said:
The easiest thing to do is just mix up a saturated dichromate solution. Keep adding water until no more will dissolve, and you have a saturated solution. You can keep this in a big amber bottle and keep adding water until the dichromate will eventually all dissolve. At that point, add more dichromate until it's saturated again. This way your mix will always be consistent. I think it will last a very long time.
Just make sure you don't shake the bottle before measuring it out for your print, or else you will get dichromate crystals in your mix.
Steve
www.scdowellphoto.com

That's great advice and will definitely make things easier and more consistent.

Colin Graham · Feb 28, 2010

Careful with saturated solutions if your darkroom temp fluctuates a lot, the saturation point can change a bit and effect the sensitivity.

donbga · Feb 28, 2010

Colin Graham said:
Careful with saturated solutions if your darkroom temp fluctuates a lot, the saturation point can change a bit and effect the sensitivity.

The saturation point does change but it has been my experience over many years that for a saturated solution of AD or PD there seems to be little effect from temperature changes as long as a large enough volume of dichromate lays on the bottom of the container.

Colin Graham · Feb 28, 2010

My ambient temp varies on average 15C from morning to afternoon, which can represent a 30% change in saturation for ammonium dichromate according to one of the sources I could find. Maybe real world results aren't as dramatic as this table suggest, but I figure gum is capricious enough already without throwing in that variable on top. I do know I had difficulty getting consistent exposures when I did use saturated solutions.

Anyway, to find the best concentration for my darkroom I just got some water as cold as my space gets, and kept track of how much would go into solution at that temp, then rounded down to the next whole number for good measure. Since I established this concentration my exposures have been constant.

donbga · Feb 28, 2010

Colin Graham said:
My ambient temp varies on average 15C from morning to afternoon, which can represent a 30% change in saturation for ammonium dichromate according to one of the sources I could find. Maybe real world results aren't as dramatic as this table suggest, but I figure gum is capricious enough already without throwing in that variable on top. I do know I had difficulty getting consistent exposures when I did use saturated solutions.

Anyway, to find the best concentration for my darkroom I just got some water as cold as my space gets, and kept track of how much would go into solution at that temp, then rounded down to the next whole number for good measure. Since I established this concentration my exposures have been constant.

Which dichromate do you prefer? AD or PD?

Colin Graham · Feb 28, 2010

I've had much better luck with AD, for both gum and carbon transfers. I know the opposite is true for many though!

sdivot · Mar 1, 2010

FWIW, I use ammonium dichromate. Can't compare the two, since I've never used potassium dichromate.
Good luck,
Steve
www.scdowellphoto.com

Loris Medici · Mar 1, 2010

I'm with Colin, I prefer to use *known/stable* solution strengths. I use ammonium dichromate at concentrations: 2.5%, 5%, 10% and 15% which are all stable (w/o crystallization) in reasonable room temperatures. (That is >= 18C/64F...) Not that it will definitely give you much more consistent results (since there are so many different critical variables in gum printing), but mind is easier that way...

sdivot · Mar 1, 2010

I suppose if you work in a garage or a basement that is not climate controlled, then you should be more diligent about your concentrations. But my darkroom is in my house where the temp is pretty consistent throughout the year. I live in Houston, so humidity is a different story entirely. I'm not sure how, or if humidity affects your concentrations. Maybe someone else can interject.
Steve
www.scdowellphoto.com

Loris Medici · Mar 1, 2010

Even if there are substantial temperature fluctuations, I don't think it will affect the dichromate solutions strength too much, especially for a large volume like Don said. The effect would be negligible indeed. OTOH, why not nailing down a variable where you can? Gum is already pretty tough to control anyway...

I also don't understand the practice of using saturated AD for making gum prints; even 15% is extreme in my experience. My usual dilution is 5% and it works like a charm with inkjet transparencies. I use 10% for single layer bleach developed prints where exposure times should be around 2-3x stronger than normal and 15% for non-oiled paper negatives . Strong dichromate concentrations tend to kill shadows too. (I use negatives with a relatively high density range BTW; negatives calibrated for trad. cyanotype.)

Colin Graham · Mar 1, 2010

I standardized on 20% AD, but count drops like any other process. I also started pre-making dispersions of watercolor pigment and gum in known and repeatable concentrations. While that's hard to measure by dropper because of the viscosity, it does measure accurately in one of those graduated cough syrup spoons and gives much more consistent results than weighing- unless you have a very sensitive scale.

donbga · Mar 1, 2010

Colin Graham said:
I standardized on 20% AD, but count drops like any other process. I also started pre-making dispersions of watercolor pigment and gum in known and repeatable concentrations. While that's hard to measure by dropper because of the viscosity, it does measure accurately in one of those graduated cough syrup spoons and gives much more consistent results than weighing- unless you have a very sensitive scale.

Well FWIW, as mentioned before I use AD in a 'saturated' state. I meter the volume with a medical syringe which seems to be very accurate. I then add an equal volume of distilled water (BTW, I always use distilled water for AD solutions) so in the end I'm using about a 15% solution. I've heard several gum printers remark that much less dichromate can be used than many people typically use including myself.

One very well known and experienced gum printer has told me about his method and he seems to use very small amounts of dichromate by comparison. But as in all things gum everyone uses what works for them.

Loris Medici · Mar 1, 2010

That's Sam I presume. (See: http://unblinkingeye.com/Articles/3CG/3cg.html) He is using an effective solution strength of 6% - I mean in terms of 1:1 gum/pigment+dichromate... I've started with 20% AD and reduced it to 5%, until I was getting good results with my procedures. Not a coincidence then...

Regards,
Loris.

sdivot · Mar 1, 2010

I do the same thing Don does. When mixing my final solutions, I measure out the same amount of water as the Am Dichromate, thus diluting it. Sometimes I substitute more gum arabic for the water as well. So the final solution of Am Dichromate is not saturated. The jar of saturated solution, used as a stock, is just for convenience.
Steve
www.scdowellphoto.com

Colin Graham · Mar 1, 2010

Many thanks for sharing your approaches, very informative. Good to know there is latitude in the process. I sometimes am too rigid to change things or explore more options once I get a little success with a certain approach.

donbga · Mar 1, 2010

donbga said:
Well FWIW, as mentioned before I use AD in a 'saturated' state. I meter the volume with a medical syringe which seems to be very accurate. I then add an equal volume of distilled water (BTW, I always use distilled water for AD solutions) so in the end I'm using about a 15% solution. I've heard several gum printers remark that much less dichromate can be used than many people typically use including myself.

One very well known and experienced gum printer has told me about his method and he seems to use very small amounts of dichromate by comparison. But as in all things gum everyone uses what works for them.

In case anyone is wondering for carbon printing - exact dilutions need to be used.

Multilayer gum printing - adhesion

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