I paint in gouache, mostly tubed, but also the Lascaux bottled “tempera” gouache. I am painting on linen on cradled birch panels with linen applied with either dilute PVA glue, or rabbit skin glue (RSG) depending on the stiffness of the linen. The linen is sized with RSG and then 4-10 layers of true gesso is applied as a ground. I want the linen for the texture.
I’ve started using gum arabic (GA) as an extender/glaze and wonder about long term cracking of the “glaze. Some of the layers are almost all GA (or 50% GA to water) as I am going for very dilute washes similar to Chinese ink paintings, and then more pigment as the subject matter comes to the forground. There is quite a bit of erasure in my process, using sponges and water, much reworking and layerring. The ground generally is preserved although to be honest I sometimes get down to the linen, or close to it. The look of “process” is important.
Q1: I suppose I assume that the interlinking of layers is preserved as all the layers are water-soluable. For example a very dilute initial glaze of 50/50 GA to water on true gesso binds well, and then subsequent layers with perhaps 100% GA glaze medium with greater amount of gouache/pigment, then perhaps pure gouache on that, possibly knocked back with a very water-wet soft brush. So you see there’s a lot of back and forth. (I’ve noticed that the GA glaze is slower to “reactivate” that a pure gouche area and I use this to layer glazes to create certain effects.) My long winded Q basically is: Does my assumption that the universal water soluability of the various layers is sufficient to create a bond between those layers, despite different amounts of GA proportionally, application of water to erase, or pure gouache (no GA at all)?
Q2: Gum Arabic is expensive. A little Windsor Newton 2.5 oz bottle is about $12. A Schminke 200ml bottle is a bit cheaper per unit, but not much. I’ve seen a thread on using photo emulsion GA on another site but I cannot find anything on the use of Food Grade GA. You can get a gallon for the $50. It’s similar in viscosity, and color. I’ve noticed that the Schminke contains “biocidal products”, which leads one to conclude that there is an issue with GA “going off”. It smells sweet, and “food-y”. I havent tried it yet but as I am starting much larger paintings I need to find a source of cheaper GA, unless you tell me my method above will lead to everything falling onto the floor in a few years. Hopefully not.
If necessary can I add a biocidal product in small amounts to preserve the food grade GA? What would that be? a few dropd of bleach?? Sounds iffy…
Thanks!
Just wondering if there are any thoughts on my Qs above? Any ideas, even if just a partial answer, would get me started.
Thanks!
Hello there,
Please consider my answer as merely a single opinion.
First I would have some concern for the longevity of painting with gouache and gum Arabic over true gesso.
Assuming ‘true gesso’ means acrylic or alkyd ground, it can have absorbency similar to paper in painting, but I fear the adhesion and brittleness of gum Arabic on these materials.
It would be prone to leave them more than it would with natural (paper) fibres. But it’s a matter of degree, gum Arabic is brittle no matter what. I would tend to think it better diffuses and adheres with natural fibres than plastic porosity.
So I would advise to look for a paper/cardboard/wood board with the texture and porosity you like, rather than building something more meant for oils and modern binders.
(Or to switch to oils diluted in retouching varnish as your painting medium. To make it work as similarly as possible, but with stronger binder and resin resilience. That is a different technique entirely though)
Q1: Solubility isn’t instantaneous, especially with cold water, it takes some mechanical action. Layers will bound to each other as they dissolve, mix and dry together, however it’s still sugar/crystal brittleness once dry. So they bond alright, but they will crack and flake also no matter what.
Q2: All the gum Arabic in solution you buy will have some biocidal product to preserve it from mould/yeast. Companies will just not mention it always (yet).
Gum Arabic is a sugar in water, you should really think of it as sweet food like other carbohydrates. So left unchecked it’s a near ideal culture broth that will grow all sorts of things.
The alternative for you could be to buy gum Arabic in a dehydrated resin chunk form. No biocide inside then, you just prepare what you need by dissolving it in water and using it before it spoils.
It might be cheaper.
As for preserving your own solution, bleach wouldn’t work long term. It only cleans water at the moment but not preserve it long term. You would need some food preservative.
What would be wise is to use boiled water for your own solution (sterilise it thus without changing its chemistry).
Good luck and cheers,
Lussh
Thank you for your response Lussh.
In fact by “true gesso” I mean the traditional skin glue/ whiting material that is a traditional ground for tempera, gouache, etc mediums. So I do not think there is any issue with adhesion long term. FWIW, paintings I did decades ago are stable and seemingly ok.
More to the point is this newer way I am dealing with gouache and the liberal use of gum arabic that is in question. Your points on GA are good ones and hopefully further discussion here might get into the chemistry a bit more. The adhesion of layers with differing amounts of paint, GA, and water is most at issue for me. Also the long term stability of the GA glaze, it’s brittleness, etc, as Lussh brings up.
The sugar issue is a good one to ponder. It’s “food” after all.The ptgs will be sealed upon completion with a solvent based matte UV varnish, after some experiments as to its affect on the color relationships, as per other threads.
As per Q2 does anyone know if there is meaningful difference between Food grade GA and artist grade? If I go forward with this method, pending other input of course, cheaper is better.
Thanks again!
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