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  #21  
Old 05-04-10, 11:00 PM
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Formaldehyde is a component of the adhesive used to help bind the fibers. Urea-formaldehyde resin was the main culprit in the 80’s formaldehyde scare. Now phenolic resin has largely supplanted Urea-formaldehyde as it outgases at a lower rate.

According to the True Gesso paper Masonite’s Duron contains no resin and thus no formaldehyde.
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  #22  
Old 06-04-10, 04:14 PM
dbclemons dbclemons is offline
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Wood made with phenol resin doesn't necessarily have to contain formaldehyde, or the amount is considered extremely low. Panels that contain urea formaldehyde resin (UF) are more of a concern, most commonly added to MDF. Formaldehyde is a natural occuring chemical in all types of wood, so no wood will be completely formaldehyde free. It's added as an internal binder in composites and plywood. There are several standards in place for building codes to label formaldehyde content that you can look for; one from California, another by the ASTM, and Europe and Japan have their own.

Long term exposure problems are unknown. It's mostly an irritant, like other VOCs. The health risks would come more from saw dust exposure (I would think) than off-gassing unless you had stacks of raw panels in your studio. I don't minimize the concern here, but you can easily protect yourself from exposure. Sizing the panel all around with polyurethane or shellac can help reduce emissions.

One other thing I would emphasize about fabric mounted to wood is that as the wood moves, either by deforming or splitting, the fabric will also move, and that can still possibly cause problems with the gesso surface or paint layer. Just having canvas on it won't necessarily solve any wood problems. It still makes the choice of wood an important decision.
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  #23  
Old 07-04-10, 07:23 PM
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"Sizing the panel all around with polyurethane or shellac can help reduce emissions."

David, if one were to do this, would the layer of polyurethane or shellac interfere with adhesion of the true gesso ground to the wood at all? I'm not that concerned myself about off gassing, but I want to understand it better for when I teach.

The end result of this very helpful and informative discussion is that I don't quite know what to tell my students. Every option seems to have benefits and drawbacks (like so much in life!). Would you wood experts sum up in a sentence or two what you recommend as the best possible support currently available for a true gesso ground and egg tempera painting?

Thanks,

Koo
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  #24  
Old 08-04-10, 02:35 AM
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I would think it best to look at the oldest surviving et's and use what they used. That said, If your work is that important in the future there will be means enough to preserve it.
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  #25  
Old 08-04-10, 01:26 PM
dbclemons dbclemons is offline
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Quote:
Originally Posted by Koo Schadler View Post
...would the layer of polyurethane or shellac interfere with adhesion of the true gesso ground to the wood at all?...
I've personally not tried polyurethane under gesso, but have for oils. It should be sanded, and I'd use water based instead of oil based polyurethane. Gesso will adhere fine to shellac, which would be my preference, and may also need to be lightly sanded first. It should be dewaxed, and I would avoid one that was bleached when used for sizing.

Quote:
Originally Posted by Koo Schadler View Post
...Would you wood experts sum up in a sentence or two what you recommend as the best possible support currently available for a true gesso ground and egg tempera painting?
I think not being forced into a single choice is a good thing, so I'd hesitate to make a single recommendation beyond what works best for me. I also like to try different things. I should be someone who makes more gesso panels than I do before I'd consider myself an expert on the subject.

What I would want in a support for gesso is something that is firm, environmentally stable, and absorbent enough to hold the glue. There are a number of things to choose from to get there, some working better than others, heavier than others, more costly, etc. As has been mentioned, some things can be combined to improve those options. The artist must decide which of those works best for them.
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  #26  
Old 10-04-10, 12:56 PM
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Hello again David,

Sorry to keep pestering you for details, but you are a wealth of information. Why would you avoid the bleached varieties of shellac? (Its what I use as an isolating layer on my temperas before oil glazing, and so bleached shellac is what I have in my studio.) Also, I recently read that shellac has a shelf life, even before its been dissolved in denatured alcohol. What do you know of this?

I agree, there are enough variables with each support and within each situation that its hard to unequivocally recommend a single one. I was just hoping for something straightforward to tell my students :-)

And while theoretically I agree with Salamander that it would be best to use what the Renaissance painters used, we don't live in a world where down the street is a panel maker who does nothing but properly cure wood and then cradle it and etc etc... While I know some people disagree with me, I think the time necessary to replicate what was done in the Renaissance is so great that doing so would make it hard to succeed financially and artistically as a painter. A traditional painter is up against a lot in the modern world. Re-creating a 15th century tempera exactly as they did (when they had guilds and traditionally trained craftsmen all around them) seems impractical. So, as you say also in your post, if I make anything worth preserving, hopefully there will be a conservator around to attend to it! And to the extent it feels practical, I do try to replicate the most important archival aspects of traditional et painting.
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  #27  
Old 11-04-10, 01:57 PM
dbclemons dbclemons is offline
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The most common method of making a clear shellac is to bleach it with alkali to the desired transparency. Another process is to just diluted it more with solvent. Bleaching makes the shellac less durable (from what I've read,) so I'd rather not use that in the foundation of the painting. I've not actually tested this, so using bleached may not matter. For layering within the painting, using bleached shouldn't make a difference. The last place I bought mine was from Homestead Finishing. They were recommended to me by a guy who makes guitars for that reason (no bleaching.)
http://www.homesteadfinishingproducts.com

The shelf life of liquid shellac can be anywhere from 6-12 months. Test it by placing a drop on glass and see if it dries hard in a couple hours. I typically try not to make more than I need or use up any extra. If your flakes or powder doesn't dissolve properly in alcohol it's likely that it's too old. Store it either liquid or dry in a cool, dry, dark location.
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