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Old 18-02-13, 08:18 PM
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Default Animal Glue

Hello All,

I know some of you are very knowledgeable about animal glues, especially framers and woodworkers. I have several questions...

Could you explain the difference between a mechanical versus a chemical bond? Is it correct to say that animal collagen glues (such as rabbit skin) bond mechanically, not chemically? If so, is this why animal glues are better for bonding porous surfaces (such as wood) versus non-porous surfaces (such as metal)? Or do animal glues bond both wood and metal equally well?

How well does collagen glue bond glass? Would you say glass is a non-porous surface like metal - or is glass a bit more porous than metal (but less so than wood)?

Do you think true gesso would bond archivally to a non-porous surface, such as a metal substrate? In other words, would you recommend true gesso on a non-porous surface (such as a copper or aluminum panel) for museum quality art (i.e. artwork that is sold for a lot of money and may end up in a public, permanent collection)?

Thanks!

Koo
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Old 19-02-13, 02:29 PM
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I'm interested to hear what others say. I don't think you can have a chemical bond to wood. Glues for plastics are most often chemical bonds I believe. Chemical bonds react with the substrates and "meld" them together... mechanical ones act more like mortar or cement. I have put true gesso on hard stone tiles and how archival that is still remains to be seen as it just hasn't been that long. I do know of an oil painter that puts gesso on his copper panels... (why I have no idea as the copper bonds chemically to the oil paints).
Thanks for the question,
Eric
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Old 19-02-13, 03:30 PM
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Well, the reason I am interested in this topic is because recently I saw a contemporary egg tempera painting on copper, and I'm wondering how archival this is. I'm talking to George O'Hanlon at www.naturalpigments.com about this. He thinks that one can paint egg tempera on copper, with or without true gesso underneath it. I know one literally can do such a thing (i.e. its physically possible to apply tempera paint to copper, as well as many other surfaces); but what I want to know is should one do such a thing (how archival is it)?

From what conservators and art history tell us, I question how well egg tempera would stick to copper in the long run, especially with no true gesso ground underneath. I also wonder, if one were first to apply a true gesso ground to copper, how well the true gesso would adhere long term to the copper. Hence my questions about collagen glue.

George seems to be saying (the conversation is ongoing) that as long as you overcome the different surface tension between the water (in tempera and true gesso) and the copper (which you can do with various additives such as ox gall and alcohol) things should adhere.

As we all know, tempera painters often look for alternatives to true gesso panels, the traditional ground & support for egg tempera. I'm happy with true gesso and don't mind making the panels, but it would be great if there were archival alternatives – it would expand the medium's range greatly. If egg tempera and true gesso both adhere long term to copper, than you’d think they would also adhere to aluminum, glass, ceramic…many other surfaces currently off limits to egg tempera (for those wanting or needing to make archival artwork.) So it seems to me this is big news for tempera painters, what is being proposed – that we can work on many other surfaces. George seems to be saying there aren’t sufficient scientific studies to confirm that other supports and grounds are archival for tempera; what I’m trying to figure out is precisely how archival he thinks these alternatives are, since he is such a knowledgeable person. Would he, for example, recommend egg tempera on copper for "museum quality" work (i.e. work that sells for a lot of money and may end up in a public collection)? That's my question to him - I'll let you know what he says.

I don’t mean to dictate that everyone must work archivally – people can and will work however they please! I just want to know what is or isn’t archival so that painters can make informed choices. I think it would be detrimental to the wonderful craftsmanship implicit in the egg tempera tradition to be compromised by uncertainty regarding what does or doesn't actually work for the long term. And for anyone who makes a living selling their art, there is the issue of merchantability – getting into trouble for paintings that fall apart too soon (i.e. Odd Nerdrum’s case). In my ignorance, when I was first learning tempera I painted atop plaster and I saw some of those paintings delaminate within a year. Thus began my cautious approach toward unproven grounds and supports.

Years ago I asked Ross Merrill, then head of conservation at the National Gallery in DC, about egg tempera grounds and support. He told me, “Egg tempera should be painted on a traditional glue gesso ground on a rigid support”. As far as I know, at this point art history and conservation science confirm what Ross said (for archival work). If anyone else has heard or seen otherwise, I’m all ears!

Koo
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Old 19-02-13, 03:55 PM
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By the way Eric, thanks for the explanation of mechanical versus chemical bonds - that helps.

I know there is a tradition of oil paint on copper panels; if the copper panels are prepared properly it is considered an archival way to work. So, as George says, if one can overcome the different surface tension between water media (i.e. tempera) and copper, would egg yolk oil stick just as well as linseed oil to copper?

I've never been able to find an answer as to what is the difference between egg yolk oil, and the various drying vegetable oils used in oil paint. Are vegetable oils stronger binders than egg oil, and that is why oil paints can be applied to more varied and less porous surfaces? Or do egg oil and vegetable oils bind equally well? And it is merely a matter that the surface tension between oil paint and less porous surfaces is more compatible? I'd like to understand that...

There is also the issue of flexibility - egg oil cures, over time, to a less flexible film than does oil paint. This is another reason to want the rigidity of traditional gesso, wood panels (and for anyone eager to paint e.t. on copper, another consideration - make sure your support is not too flexible.)

Well, I've gotten off on a lot of different tracks here, which may necessitate a separate "ET on copper" posting! I'm still most interested, in this post, in the questions about animal collagen initially asked, so many words ago...

Koo
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Old 21-02-13, 03:26 PM
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"In my ignorance, when I was first learning tempera I painted atop plaster and I saw some of those paintings delaminate within a year" I did the exact same thing and have the remnants still of my peeling painting...
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Old 21-02-13, 03:48 PM
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HI Koo, Another option that I have run across recently is Arches "new" oil painting paper. I needs no gesso. and, as far as rigidity can be glued to a rigid surface.
-Eric
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Old 24-02-13, 08:37 PM
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Good questions Koo. I just went over to my glue pot, and no glue is adhered to the aluminum pot, though I am not "neat". Checked my joining vise; the glue droppings can be popped off of the cast iron surface with ease. But, hide glue is also used for "chipping" glass, where a high strength glue is brushed on the surface of glass, and as it dries, shrinking, it pops a piece of the surface of the glass off, ... but my experience says hide glues will not adhere well to non-absorbant surfaces. Since hide glues do not change chemically when drying, there needs to be some mechanical bond: absorption, a well fitted joint, a roughened surface. Droppings of glue on the hardboard surface of my studio floor remove wood when scraped or chipped off.

Egg has a tenacious bond; I use a glass palette, and if I let dried paint sit on it, it can be a chore to scrape off.

My opinion is that traditional gesso would not work on a copper plate, even if there is a roughened surface, but that egg tempera would probably stick quite well. My other opinion is that hard board is about as much innovation as I'm willing to use.

My very unscientific answers to your questions. Looking forward to hearing what happens if somebody does some experimenting.

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Old 25-02-13, 04:09 PM
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Hello Bron,

I know you've had a lot of experience with collagen glues, so your insights are very helpful - thanks!

I've been doing lots of research on the various questions I pose here, and have spoken to a couple of conservators, including the egg tempera conservator at the National Gallery, who was also Andrew Wyeth's conservator. All the resources I've consulted agree that animal glue needs a porous surface to adhere well; and that egg tempera does best on an absorbent, true gesso ground. They also mentioned the incompatibility of water based media on metal supports - too non-absorbent, and prone to corrosion or rust when exposed to moisture.

However George clearly feels egg tempera and true gesso can be safely applied to non-porous, non-absorbent surfaces, and these surfaces would be fine for "museum quality art work", so to speak (i.e. work that needs to last....). He points out the problem of humidity in wood and true gesso, both of which tend to absorb moisture and change shape, which is problematic for a brittle medium such as tempera. A point well-taken. And yet, the conservators are clearly in the other camp....

So I remain confused; the chemically un-sophisticated artist, caught between two respected sources of knowledge! For now I will err on the side of tradition, conservation science, and consensus and continue to work on true gesso, wood-based panels (and, given that they provide such good working properties for tempera and I am happy to make them, this is not a problem for me). But art history is, among other things, a history of creative experimentation leading to new ways of working, and I'd love to see egg tempera find a wider audience. I am always eager to hear more, reliable support for new ways of working.

Koo
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Old 27-02-13, 08:30 PM
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Default Animal Glue

Koo, thank you so much for going over all of this, it's fascinating!! It's great to have everyone's input as well, including George's.

Mona
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Old 28-02-13, 02:36 PM
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I pointed Hugh Phibbs, a conservator/preservator from the National Gallery at this thread. He regularly answers tech questions on the picture framers forum, The Grumble. His response below.

My own thoughts, random, from an unscientific, but experiential basis is that ET directly on a metal substrate would work. Hide glue gesso would be a problem, though. One of the advantages of hide glue when joining finished frame moldings is that glue squeeze out had little adhesion to the finished surface. As I've mentioned, hide glue does not stick to the aluminum glue pot.

There is an atypical Winslow Homer painting at the Krannert Art Museum, U of I, Champaign/Urbana; an oil on panel. The panel has no visible ground, and in fact the color of the wood (probably mahogany) is an element of the painting, showing through as a color.

Hugh's response:

"That is a very interesting forum. There are so many issues raised by that thread that it is hard to keep them all sorted out. To me, a chemical bond is one in which a chemical change is initiated by the application of the adhesive and it “welds” the parts together (welding, soldering, hot glue on the appropriate plastic, etc.). When we think of how smooth surfaces really are, it is worth remembering that glass has micro fractures all over its surface, which is probably why hide glue sticks to it. Metal is crystalline, because each of its atoms is bonded to its neighbors, through metallic bonding. I know how well oil paint sticks to metal and wonder whether an oil ground could be used for the lowest layer in a tempera panel, which used a metal support material. An animal glue gesso could be applied over that (the reverse of a traditional oil painting) and then the tempera. This should be tested before anyone uses it, but nothing violates well-tested combinations of materials.

Thanks for pointing this out."

My feeling is that the hide glue gesso would be an unnecessary addition; and that the color of the metal substrate could be used to advantage. ET directly on a roughened metal surface (220 or even finer grit; the surface needs to be clean, not oxidized, and have some texture) would be fine, and as archival as the vagaries of life allow. Of course, now I'm going to have to get some copper or brass sheet, and fool around with this. And then wait a few hundred years to see how it holds up.

Last edited by Bron; 28-02-13 at 02:39 PM.
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