Shelf Life of Gum, Pigment, Dichromate Stock Solution

Andrew O'Neill · Dec 27, 2018

I'm beginning to realise that keeping a stock solution of gum, pigment and the dichromate (for tri-colour prints) for a week or so, results in a print with more grain and less detail, compared to a print made from fresh solutions. Anybody else work from stock and noticed this? To me, it looks like keeping qualities are very poor. I keep mine in glass jar, in the dark. Maybe Bob Carnie can comment...
Thanks!

Andy

jim10219 · Dec 27, 2018

Are they all mixed together, or separate? Powdered pigments or watercolors in tubes should last decades. Potassium dichromate in powdered form should last a long time as well. Even dissolved in water, it should last a long time if kept in the dark. I've had bottles last longer than a year. Though I use super saturated solutions, so I often have to reheat and remix the solution, as crystals will reform along the bottom after a few days. I use commercial gum Arabic that comes with preservatives, so it also lasts a few years if stored in air tight bottles in the dark. I only mix them together right before coating the paper, and do that a few hours before exposure. I've never had any issues with increased grain or loss of detail.

But if you are, I'd think the most likely causes are either using old gum Arabic that's been tainted by mold or bacteria, or a change in your process. I know fresh mixed gum Arabic from powder doesn't last long without a preservative added. Graininess and loss of detail could also be the result of too much agitation during development, or the Gum not hardening enough. That could be the result of not enough exposure, not enough potassium dichromate in your mixture, or old gum Arabic. It could also be not enough tooth on your paper. It's hard to say without examples. Gum Bichromate is a tricky process that is anything but predictable. I usually print 4 and may get one "keeper". No two prints are ever alike.

adelorenzo · Dec 27, 2018

Per Christina Anderson's book the fully mixed solutions will last at most a day or two. I have sometimes put on a layer from the day before but usually less than 24 h old. Generally I mix fresh each time.

The dichromate and gum/pigment solutions on their own keep quite well AFAIK. Mine are at least a year old and seem to be working fine.

Andrew O'Neill · Dec 28, 2018

I am aware of the shelf life of all ingredients stored separately. It is when they are combined together that I was unsure about. The gum is quite fresh. Mixing as needed is how I will proceed from now on. Thank you all!

Herzeleid · Dec 28, 2018

I kept gum-pigment mixtures with extra sodium benzoate for months (some pigments i.e ivory black, spoil faster than others) but never with dichromate. If I recall correctly it would keep for one or two days before dark reaction takes over. I mix stock gum&pigment with dichromate 1+1 prior to printing.

Some gum printers use polyvinyl alcohol instead of gum arabic, PVOH and dichromate solutions can be stored for weeks to a few months in refrigerator before dark reaction takes over. Duration depends on dichromate concentration.

Dan Pavel · Dec 28, 2018

Andrew O'Neill said:
I'm beginning to realise that keeping a stock solution of gum, pigment and the dichromate (for tri-colour prints) for a week or so, results in a print with more grain and less detail, compared to a print made from fresh solutions. Anybody else work from stock and noticed this? To me, it looks like keeping qualities are very poor. I keep mine in glass jar, in the dark. Maybe Bob Carnie can comment...
Thanks!
Andy

I've noticed that, too. Now I'm using a digital Jewelry Scale, only mix the solutions as needed for one print and use them within an hour after mixing. I've noticed that even if used 4-6 hours after mixing the quality of the print begins to suffer.

I've noticed that the humidity of the paper (or of the gelatine layer on the paper) while applying the gum solution makes a difference, too. A slightly moistened gelatine layer visibly reduces the grain and stain of the print. That's why I uniformly moisten the gelatine side of the paper with a brush, let it semi-dry for ~5-6 min and then apply the gum solution. Probably the gelatine absorbs the water and it's swelling a bit making a more compact background layer for the gum solution.

Bob Carnie · Dec 28, 2018

Andrew O'Neill said:
I am aware of the shelf life of all ingredients stored separately. It is when they are combined together that I was unsure about. The gum is quite fresh. Mixing as needed is how I will proceed from now on. Thank you all!

Hi Andrew

if they are mixed together I would think a very short shelf life, I call this a working solution, and in my space I mix each day and never leave for next day even if I have mixed too much.

If you are talking stock solutions (which I read as the Gum, Pigment mixed with Gum, and Amomonium Dichromate well my stuff lasts a very long time, I bought a case of gum and it lasted three years actually on last bottle and using today and will work well, the pigment in gum solution needs an weekly shake if I want it to not harden and separate in the bottle. Ammonium Dichromate 10% well I mix a litre and it goes on and on.

the AD mixed with Gum will try to harden with any exposure to light as it should therefore I would not pre mix a working solution and use over multiple days..(PLEASE READ IMO only ) others may have found different .

Andrew O'Neill · Dec 28, 2018

Thanks Bob. I think keeping the mixed solutions over a few days spells disaster. I found this out after a lot of waste. One positive thing though... Hahnemuhle Plat Rag is a wonderful paper for gum. No size required (at least for tri-colour).

Andrew O'Neill · Dec 28, 2018

Thank you, Herzeleid, and Dan.

jim10219 · Dec 28, 2018

As Bob does, you could pre mix the pigment and gum. Watercolor paint is basically just pigment and gum Arabic. And you could premix your dichromate and water. That would give you two liquids that would keep fairly well and allow you to quickly mix them to a working solution.

Andrew O'Neill · Dec 28, 2018

Thanks Jim. As a carbon printer, I've been quite used to keeping stock solutions of dichromate of varying percentages... But keeping stock solutions of only gum and pigment never crossed my mind. I will as of today. Onward and upward!

Bob Carnie · Dec 28, 2018

Andrew O'Neill said:
Thanks Bob. I think keeping the mixed solutions over a few days spells disaster. I found this out after a lot of waste. One positive thing though... Hahnemuhle Plat Rag is a wonderful paper for gum. No size required (at least for tri-colour).

Just a pre shrink its is a lovely paper

Andrew O'Neill · Dec 28, 2018

Yup, it sure is. I double shrink, using very warm water (soak for a couple hour, dry, then soak for another couple hours). I found boiling water to be hard on the paper fibres.

BJ68 · Jan 8, 2019

Little tip for gum/pigment stock solutions: Add a couple of 4 to 5 mm glass beads. Has the advantage that the mixing is easier and if the pigment sediments to the bottom of the bottle, the resuspension with shaking is much more easier, because the stuff sticks on the glass beads and not on the wall.

Edit: Steel beads are not a good idea; corrosion....own experience

Bj68

Andrew O'Neill · Jan 8, 2019

That's interesting. Thanks, Bj68. I've been mixing small quantities of gum and pigment... 5ml, which is enough to make 4 8x10 prints after dilution. Getting more "consistent" results.

Aimee Danger · Sep 7, 2019

Andrew O'Neill said:
Thanks Bob. I think keeping the mixed solutions over a few days spells disaster. I found this out after a lot of waste. One positive thing though... Hahnemuhle Plat Rag is a wonderful paper for gum. No size required (at least for tri-colour).

I’m on the hunt for the perfect paper that doesn’t require sizing after preshrinking OR doesn’t shrink. Hahnemuhle Plat Rag, you say? 300? How would I ask for this in the art store?

Andrew O'Neill · Sep 7, 2019

Aimee Danger said:
I’m on the hunt for the perfect paper that doesn’t require sizing after preshrinking OR doesn’t shrink. Hahnemuhle Plat Rag, you say? 300? How would I ask for this in the art store?

I get mine from a photo store, downtown Vancouver, BC. My local art stores do not carry it... but you could ask yours if they could bring some in if they don't carry it. This paper does shrink, so you must preshrink it if you plan on multiple passes of gum. No extra sizing needed whatsoever. It's now my go to paper, even for carbon transfer printing.

Bob Carnie · Sep 8, 2019

Aimee Danger said:
I’m on the hunt for the perfect paper that doesn’t require sizing after preshrinking OR doesn’t shrink. Hahnemuhle Plat Rag, you say? 300? How would I ask for this in the art store?

all the major photo stores will post where you can buy HPR- Bostick and Sullivan does stock it as you are in the States.... getting it in Canada is a real problem, the Canadian Distributor does not stock ample supplies and is a real problem for us Canadian Printers.. Hopefully the manufacturers will see this problem and find a better solution for us Canucks.

Bob Carnie · Sep 8, 2019

to the original post a bit ...... Russell Monk is here printing for about a month and has done a lot of prints... one day he made the mistake(IMHO) of coating in the afternoon and then leaving overnight the coated paper ... the next day he decided to print.... I was mortified and thought that he had fucked up all the coated prints...

What did happen was his washout time increased by a 100% factor or double the time... In my workspace a gum prints washes out in less than 10 min ..

So what does this tell us... Ammonium Dichromate and gum mixed together even without light will/seem/maybe starts to react and harden the gum.. I imagine if the lights were on even though tungstan the effect would be more pronounced.... One of the most important aspects that seems to be overlooked by the teachers of gum printing is this physical reaction of the gum hardening and holding the pigment in place, much like when you were a child and you wiped your nose with your fingers and some of the more stickier snot stuck.. now I only refer to this as being a child as a grown up I would never use my fingers now to pick my nose.

For those gum printers .. this is the crux of gum printing and the most important fact... the gum hardens.. the pigment stays.................This is almost the same kind of logic as how does Pyro seem to record detail better... well its due to the tannin effect of the silver hardening as it develops out creating concentric patterns of detail..... look at a pyro negative in off light and look at a multiple gum print in off light and you will discover the most important factors in both methods of production. YOU CAN SEE A RELIEF PATTERN .

Shelf Life of Gum, Pigment, Dichromate Stock Solution

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