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technical question

Post #644 • October 13, 2005, 7:28 AM • 25 Comments

I want to try a method in which I glaze over monochromatic, heavily impastoed underpainting in oil. My experiment looks promising, but the underpainting is taking an unacceptably long time to dry, even though it's heavily laced with Galkyd Gel. After a month, the thicker areas are still soft to the touch. So, two questions:

1. Does anyone have any information about archival problems with using oil-based glazing media on top of acrylic paint? It seems like it would be a bad idea to put a petrochemical solvent on a flexible acrylic polymer, but I've also seen plastic gasoline cans, so I don't know.

2. Can anyone help me put my finger on why liquid acrylic medium just doesn't freaking look like an oil glaze, and what to do about it? I'm thinking of a 50/50 mix of gloss and matt medium, and slapping a coat of it on the underpainting before going on top with an overpainting of acrylic paint and the same medium to try and get some, I dunno, some atmosphere in there.




October 13, 2005, 8:44 AM

I can give you two semi-unsatisfactory answers.

1. Oil is supposed to be fine on acrylic, but if the acrylic is still wet there could be a problem. I don't know what "Galkyd Gel" is, but why not use just plain Gel, modelling paste, gesso or whatever, tinted to taste? These will give you any kind of impasto you want and will dry pretty firm in a day or so.

2. Acrylic is different. The best thing to do is learn to love plastic.



October 13, 2005, 9:02 AM

1.gesso is white...unless you want white, then it's a bad suggestion. Then again, a very watery & thing gesso veiling the ground beneath can produce a nice atmospheric effect....But the trick is thinning...

2. Galkyd is an alkyd resin hardens like tree sap. Painting with it over acrylic should be no problem at all unless the acrylic is wet, in which case it won't bond well. (i've seen "wrinkle" over moist acrylic..a cool effect if you don't mind, but not desirable if you do.

3.Check out the Gamblin Paint (out of portland oregon) website...It explain things very well...



October 13, 2005, 9:30 AM

Acrylic is different.

I know, I just hate it when I have something observable like that in front of me and I can't pin down the difference. It makes me wonder if I'm talking myself into seeing something that isn't there.

Galkyd Gel is IMO the best impasto medium for oil. Galkyd in general is Gamblin's proprietary alkyd line.

...learn to love plastic.

If it's that, or make one painting a month while I wait for each one to dry, I could.



October 13, 2005, 9:38 AM

Love plastic? Actually when linseed oil polymerizes it does it in a fashion that is very similar to acrylic.

Re: #1, the only instance where oil really sticks to water based acrylic is when the acrylic has been significantly dulled. The sure fire way to achieve this is to add calcium carbonate or a similar substance (as they do in acrylic gesso) that opens up the surface so the oil can flow into the microscopic fissures and get a physical grip on the otherwise slippery and impervious acrylic after it has polymerized. The problem is that each medium shrinks and contracts at a different rate when exposed to moisture in the air, temperature changes, and its own aging process. Then of course, there is the problem of movement of the canvas if that is the support.

About Galkyd Gel: I just began investigating it this week. So far it sucks. "Galkyd" is Bob Gamblin's trade name for alkyd resin. Alkyd is a wonderful substance for painting. While basically linseed oil, it has been altered to be much more resinous (hence no need to add damar or other gums to the mediusm), much more flexible, and much quicker to dry than straight linseed oil. But Galkyd Gel does not dry fast, even when brushed out very very thin (after 4 days it is still sticky and gooey). Don't know why. I would guess that applied thick, as the name suggests and Franklin has apparently done, it would be much worse. Gamblin markets a great painting medium called Galkyd Lite that fulfills all the promise of alkyd plus it is wonderfuly fluid and completely free of milkiness. Liquin, Winsor Newton's name for alkyd resin, comes out the bottle with the consistency of snot (some like that) and is milky. If you brush around in it, it will loosen up from the friction created by the brush. The milkiness is not a problem at typical paint film thicknesses. You can alleviate the milkiness by adding a tad of alcohol, I'm told, but have never tried.

#2. Golden makes a glazing medium that has some limitations (you can't put it on too thick, for instance) but it is very brushable if you can stand the floppiness that acrylic always induces in even the finest brushes. You can also up the humidity in your studio and/or make a humidifier that hovers over your pallette and area of the canvas you are working on.

That noted, there are two kinds of acrylic.

The common one is suspended in water which keeps the molecules from touching each other. As the water evaporates, the molecues touch and chemically bond to form very long stable polymers that can never be diluted by water again. Before drying, it is very milky even at paint film thickness so what you see is not what you get if very much of it is present in the paint.

The less common acrylic is soluable in mineral spirits and turpentine - probably other similar solvents as well. It is very resinous and when dry is also flexible. And it does not rot canvas or paper. Morris Louis used it exclusively as his medium for his major work. Unlike both oil and waterbased acrylic it is water clear before it drys. A glass of it looks like a glass of water, except that it is much thicker. It is used as a final archival varnish for both water based acrylic and oil paintings. It is called "spirit acrylic" or "mineral spirit acrylic" and sold by Golden as MSA Varnish. What you see when you paint with it is exactly what you get.

Its "problem" is that it remains forever soluable in turps or mineral spirits. (Turps affects it more quickly than mineral spirits, as turps are approximately twice the solvent, compared to whimpy mineral spirits.) That is why it works as a final varnish. It can easily be removed.

MSA sticks to water based acrylic and I have used it for that with great success as a varnish.

I also use it to paint pictures. I usually size the canvas with rabbit skin glue but I have also used it with half rabbit skin/ half acrylic medium sizings, and even pure gesso. I often stain the canvas intensely first with thinned out water based acrylic in either black, red, yellow, or violet (which means there is a lot of pigment and a significant amount of acrylic medium) - followed by rabbit skin. Used straight, the latest coat of MSA based paint has a tendency to dissolve the previous coat somewhat - not always bad, either. But if I add some alkyd resin to the mix, this tendency is greatly reduced. If you want to use it as a traditional "oil glaze" I recomend adding alkyd if you do not like the tendency to dissolve the undercoat.

Standard oil paint will dissovle fine in MSA, but you can also use dry pigment to get your color. Theorectically, "universal" colorants put up in ethelyne glycol would also work, but I am unconvinced of the ability of the EG to evaporate before the film closes - don't want antifreeze in my pictures. And the only stable universal colorants are the earth colors.

If I'm using dry pigment I wet it first with turps, then add the MSA (plus, most of the time, a bit of alkyd) and stir it up good with a piece of slightly bent coat hanger mounted in a 30 year old Black and Decker drill. I'm not sure if it would work with a modern drill.



October 13, 2005, 9:42 AM

How about building up an acrylic underpainting with a marble dust included--thinking of venetian plaster. This will give you the tooth needed for the oil glazes to grab onto.

Have you tried the Daniel Smith alkyd resin? It has a uniform satin finish. I find Galkyd more glossy, which may or may not allow you additional uniform layers of glaze.



October 13, 2005, 9:55 AM

Bob, in many experiences with Galkyd and other forms of alkyd, both student work and my own, there is no problem with multiple coats sticking to each other. I expect Galkyd Gel to not be an exception either, if and when it dries.



October 13, 2005, 10:00 AM

A picky response to Franklin's reference to "petrochemical solvent". Turps comes from pine trees and is a very good solvent for linseed oil, which comes from flax seed. Everything is a chemical, in the end. Nothing special about those that are found in oil. Many of them intermix well with "natural" chemicals. (Picky point #2: Everything that exists is natural.)



October 13, 2005, 10:29 AM

I have had problems with Galkyd cracking. Not the gel, but the more liquid medium. That can be solved by painting on board, I suppose. But if you're going to paint impasto, why use a medium? Gamblin paints generally come out of the tube thick enough to put on with a knife without any additional thickening, and will usually dry in a few days to a week unless you're using a lot of titanium white or cadmiums or cerulean. But if you're making monochromatic impastoed unterpaintings, I'll assume you're using a fair amount of white. Lead white dries fast, so if you want to die sooner...

Archivally speaking, a thin glaze over a thick underpainting is a bad idea. Remember "lean to fat" from intro to painting days? Even if the thicker underpainting feels hard and dry after a few weeks or even a month or two, chances are it's not totally dry. Putting a thinner layer of paint over that will dry much more quickly and still have the wet paint underneath. Never a good idea if you want your paintings to last into the next millenium.

But who wants their paintings to last that long, anyway? So just make sure they won't fall apart in ten years and you'll be fine.

Painting with oil over a permeable layer of acrylic should be fine if you let the acrylic "off-gas" for a couple of weeks.

And if you're trying to get an oil look with acrylic, use Golden. It'll never be the same, though. It will always feel and smell (the worst part) different.



October 13, 2005, 11:18 AM

Thanks for all the good suggestions. It seems that putting Galkyd Anything on top of an acrylic painting of any depth would violate the fat over lean principle. That's why I thought there might be something in the literature advising against it, but apparently not.

Catfish - Liquin loosens up a little bit with plain old turp, so you don't have to fool with alcohol. I agree that it feels and looks like snot. The Galkyd Gel is more clear and dries a little shinier, and normally dries acceptably if you're not adding anything onto the surface. As an underlayer or middle layer, I don't know.



October 13, 2005, 11:31 AM

It seems that putting Galkyd Anything on top of an acrylic painting of any depth would violate the fat over lean principle.

I'm not sure I understand this sentence. Acrylic is as lean as it gets because there's no oil in it. Lean to fat applies to oil content and drying time. You want leaner oil underneath fatter. Acrylic has no oil, so if it is totally dry (even though acrylic can dry to the touch in minutes or hours, thicker acrylic should wait a couple of weeks, probably, if one is trying to maximize arcival quality), painting over it with oil or alkyd would not violate anything.

I could be misunderstanding the reasoning in that sentence, though.



October 13, 2005, 11:47 AM

Lean oil films do not have the gripping power of fat ones. That, combined with the difference in shrink rates as they age, allows the lean layer to separate from the fat one. Adding damar resin aleviates this somewhat because damar is eternally soluable in turps and. assuming the leaner layer contains some turps, it will etch the fat one underneath and increase the grip. Damar in the lean layer, while making it even leaner, adds to the grip there too.

Myself, I have found that it takes a pretty flagarant violation of the "fat over lean" principle to make a visible difference. Much more likely to screw up with aging is heavily impastoed oil paint no matter how well applied. If you want to paint thickly, water based acrylic is the most durable choice. Hofmann owners have complained to me about the high cost of maintaining his pictures. Some Clyfford Still pictures have the same problem. Adding too much drier is another way to get problems; they accelerate the aging process. Some say don't ever use them.

Anyway, the "fat over lean" principle applies only when both layers are oil based. Acrylic is the ultimate "lean" in that it contains absolutely no oil, so any percentage of oil over the top of it is in accordance with the gross reading of the principle. But ... putting oil over acrylic does not work unless the surface is pitted. As you know, standard gesso is acrylic based, and oil sticks to it just dandy, thanks to the pits.



October 13, 2005, 12:16 PM

The whole idea of the fat over lean principle is to put more flexible layers over less flexible layers. (I illustrate the point to students by imagining that they've painted a trampoline with housepaint, letting it dry, and jumping on it.) Although acrylics contain no oil, they're still much more flexible than layers of dried oils, so even if you get around the inter-coat adhesion problem (marble dust, etc.), and assuming that nothing in the oil will attack the acrylic, it seems that you'd still be violating fat over lean. On a board, with a thin layer of acrylic, it shouldn't matter, but an impasto layer of acrylic seems like it would cause a higher layer of oil to crack.

Interesting that we all agree that acrylic-medium glazes don't look like oil glazes, but we haven't heard why yet. It's not just me, then; good...



October 13, 2005, 12:50 PM

I had a student once who put a final very thin yellow ochre glaze over his acrylic paintings. He called it "unifying with yellow" and it fooled many people into thinking the picture had been done in oil.



October 13, 2005, 12:57 PM

Fat over lean has as much to do with shrink rate and grip strength as it does with flexibility. So, you can expand that lecture some. And hope no one asks you why acrylic gesso is OK to use before oil. So far you have explained why that should not work.

When housepaint is formulated, little attention is paid to flexibility because all its presumed supports are rigid. That's one reason why it is not good to use it for paiting on canvas. The other reason is many of the pigments used are fugitive. (But many use it anyway, sometimes to aesthetic profit.)

Pick. pick.



October 13, 2005, 2:22 PM

What about applying an oil glaze to a plaster or wax relief on hardboard or luan.



October 13, 2005, 2:35 PM

That would be interesting in and of itself, Johnny, although plaster's a bear to have around in your life (fragile, heavy, requires boards) and because of the heat in Florida, encaustic isn't a lot of fun down here, slaving over a hot stove and all. I've seen an encaustic displayed in a storefront window in Miami, in air conditioning, melt in the sunlight.

I'm leaning towards an all-acrylic solution here. The yellow ochre thing already occurred to me, and it I think I'll just fiddle with the mediums until they suit me so that I spend the maximum amount of time painting, at room temperature, and the least amount waiting for stuff to dry. Thanks to all for the help.



October 13, 2005, 4:02 PM

Oil over acrylic will work, especially if the acrylic surface isn't super slick. Fat (oil) over lean (acrylic) is maintained but the new oil layers must maintain the fat over lean principle. This issue is partly flexibility but it is also due to adhesion, fat bonds to lean but an oil wash over a fat layer is fragile and can be the point of failure if you put a fat layer over it. I recently rolled up some 15 year old paintings with rather thick surfaces made this way with no problems

I've been using a Kremer alkyd, and more recently Galkyd on the bent metal paintings. It's bulletproof, really sticks to the primer so it should be fine over acrylic. I don't know about cracking as I use a rigid support.

I'll bet the difference between oil and acrylic glazes is the molecule size of the binder. An acrylic glaze is thicker and has a ever so slight color. Also I suspect that in all transparent mediums the refractive index will change the appearance. Adding wax will kill the gloss in Galkyd it also chnges the reflective quality (to the better IMHO) because wax has a microfine crystalline structure which breaks up the light differently.



October 13, 2005, 4:27 PM

In #17, "made this way" meant oil over acrylic paintings.
and the oil glaze has the slight color, not the acrylic.



October 13, 2005, 5:07 PM

It just occured to me that a fews back i came upon a Larry Poons at a local auction house. Fairly small (3'x2'), in greys, from either '81 or '83. It was ugly and i bought it since no one knew what it was.

It was heavily buit-up layers of acrylic or oil on top of foam on top of canvas/linen; it looked like the surface of the moon. It was a dust magnet. In fact, Franklin didn't you experiment with expando-foam before?

Anyway, another idea to throw your way.



October 13, 2005, 6:23 PM

I don't know what you paid, Bob, but you probably got a lot of art for the money.



October 13, 2005, 6:31 PM

Just an idea but what about
an old 60's stain painters medium like Magna Acrylic which is diluted with terp and applied in washes?
Although I do not know if it is still made or sold?
Has anyone ever used it?



October 13, 2005, 6:44 PM



October 13, 2005, 6:53 PM

I used magna for a couple years. It was great because it was clear, like plastic honey, and it carried pigment around beautifully, but it was nasty, toxic stuff, smelled bad and you never got rid of the smell and clean up was very difficult. Also it tended to get brittle after a few years and did not adhere to acrylic very well, at least back in the early 70s. Golden has something called Tar gel which is similar and not so evil.



October 13, 2005, 7:03 PM

Lots of good technical information from Golden Paints here



October 13, 2005, 9:47 PM

Acrylic under oil has a tendency to crack over time, depending on the thickness of the oil. I liked the effect initially but did not like the little chunks falling off as the years went by. rabbit glue primer sometimes rots canvas but is so nice and tight. then put the lead white on top but if you are mixing dust pigment it's toxic so use a mask. Mixing damar crystals (in cheesecloth) into terp and then adding linseed oil and dry pigments gives me greater control over thickness, fluidity, and color. just don't mix a big batch at once b/c then you have to keep diulting with terp and remixing daily. keep in tightly closed jar. i love to use encaustic also (use a hotplate away from where you are working b/c toxic fumes, wear a little mask) (no wonder artists that use foam, etc get cancer) (poor eva hesse)...



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