Egg Tempera Forums

Go Back   Egg Tempera Forums > The Forums > The Forum for Tempera Painting Issues

The Forum for Tempera Painting Issues Sharing the knowledge and experience of fellow tempera painters.

Reply
 
Thread Tools Display Modes
  #1  
Old 27-03-10, 05:07 PM
Paul B Paul B is offline
Member
 
Join Date: Feb 2008
Location: Norfolk England
Posts: 32
Default Simple Gesso Panels.


I am close to giving up on tempera painting. This is because of the difficulty of somehow finding myself in the same room as a decent gesso panel. I have tried using wood but I do not have the time or carpentry skills or time to produce the complex bracing for the back. I was surprised at just how active a piece of wood is.
I was reluctant to use MDF as I saw this as a cheap horrible material. My paintings are expensive so I have always felt guilty about the thought of selling paintings made of it. I would not dream of doing my oil paintings on it. Perhaps there is no alternative, and perhaps it is not that bad after all, but I cannot find a supplier of low emission MDF in the UK. If I use MDF should I coat both sides with gesso before adding a supporting structure to the back? Does anyone know about the possibility of the lignin seeping through over time?
The Simon Liu Inc panels with the 'Baroque' supporting back mentioned in the recent thread confused me as they have bracing on the back making it impossible to put an even coat of gesso on both sides thus instantly causing tension in the panel? Perhaps they are not for gesso.
The alternative is buying a ready-made panel. Does any one know of an excellent supplier here in the UK? The problem with that is I may not know what went into making it. I want something reliable and of a very high standard.
I just want one simple but totally sound method that I can use for the rest of my life and stop all this messing about and time wasting. I am willing to spend quite a lot of money on each panel. I dont want to compromise.
On a positive note I have no problems applying the gesso itself.
Sorry this is so basic. I would appreciate any help. You could possibly save me form egg tempera free future.
Reply With Quote
  #2  
Old 27-03-10, 11:18 PM
DLH's Avatar
DLH DLH is offline
Senior Member
 
Join Date: Dec 2004
Location: Detroit
Posts: 123
Default

Abandoning tempera would be no solution to my painting support issues. The archival stability of traditional gesso panels makes them superior for oil painting as well. Stretched canvas is a particularly poor support. Canvas loses most of its structural integrity in a century or so. It might even be said of many old paintings it is the paint film that supports the rotting canvas rather than the other way around.

Paul, I share your knee-jerk distaste for MDF and other engineered wood products made from reconstituted wood fiber. While my objection is partially aesthetic there are practical reasons as well. As I stressed before, wood in its natural state swells and shrinks with seasonal changes in humidity. Fiberboard moves with moisture changes as well, but while natural wood returns to its former size when it dries out, fiberboard does not. This is due to the way it is made. A 12mm MDF panel begins with a blanket of fibers maybe 120mm thick. Then it is pressed between heated platens under tremendous pressure. Were they not held in check by adhesive the blanket would regain much of its former thickness when the pressure is released. When humidity swells fiberboard its adhesive bonds are weakened. Even when the humidity goes down the panel never returns to its former size. This might not be a problem if the panel moved uniformly. However, wood panels absorb moisture much more readily from the edges than from the field. This is why it is stressed that the panel edges be sealed. While sealing greatly slows the inevitable edge thickening it does not stop it.

Systems like the dovetail braces employed in the Pandora panels and the attached movable grid used by Simon Liu are not intended to prevent the panel from changing size. They aim to keep the panel flat regardless current moisture content. I’m not sure about the Pandora system but the Simon Liu panels are not intended to be gessoed on the back. The reason unbraced panels have gesso (and paint) on the back is so both sides will take up and release moisture evenly. Otherwise the side that absorbs more readily would swell faster causing the panel to warp. Well-engineered bracing prevents this.

My choice for support material is plywood. It is made of alternating wood veneers with the grain of each layer at right angles to its neighbor. Because moisture movement does not apply parallel to the wood grain each veneer locks those next to it, effectively eliminating movement in the length and width of the panel. The thickness will change but that does not cause warping, and the veneer is natural wood it does not suffer the ratcheting effect of fiberboard. The species and even the quality of the wood used for the veneers does not matter much. What does matter is how carefully and well the veneers are glued together. Poor glue or technique can allow veneers to delaminate. Poorly made plywood sometimes has excessive internal voids, or worse overlapping veneers. I generally use 12mm cabinet grade hardwood plywood for panels up to about a 1/2 square meter. It typically has internal veneers made of poplar with thin decorative veneers of prized wood on the top and bottom. Probably the best material for painting panels is marine grade Mahogany plywood. True Mahogany has one of the lowest moisture size change ratios.

Last edited by DLH; 28-03-10 at 08:19 AM.
Reply With Quote
  #3  
Old 28-03-10, 02:47 PM
dbclemons dbclemons is offline
Senior Member
 
Join Date: Mar 2006
Location: Texas
Posts: 227
Default

Quote:
Originally Posted by Paul B View Post
...I was surprised at just how active a piece of wood is...
Although all wood has movement, they don't all move to the same degree, so I might question the type you have seen. I applaud your concern with quality, but don't judge all wood by the poorest examples.

The benefit of composite panels (HDF & MDF) is they are smooth and regular without the risks of spitting, voids, or grain issues of solid wood or veneer. They also are more dense and heavy with the risk of chipping at the edges, and the thickness of MDF helps reduce movement. I've seen MDF up to 1 inch thick (can be up to 4",) which isn't going to move at all, but would be as heavy as concrete. Thinner widths (and all HDF) are more likely to curl or twist and require bracing. The biggest concern for me with composites is almost all are made of poor quality materials. That issue can be reduced by properly sizing it, and using it just as support for canvas or rag paper. When you're not sure what the panel is made of, that would be my recommendation.

I would agree with Doug on choosing plywood; although, for me the choice of species is critical. Birch is the most common and is adequate, but maple, ash, poplar or other hardwood species are more stable. Just like composites, thickness adds stability. Another approach is to sandwich a MDF panel between two layers of veneer, front and back, giving you the benefits of both.

Although I'm not personally familiar with products from Zecchi (Florence Italy,) but I often see them recommended as a decent brand supplier, and they make gesso panels. I suspect they have distributors in the UK as well.
http://www.zecchi.it/

Personally, I can't guarantee any company will be around for my whole lifetime, so it's better to rely on my own abilities, especially when what I can make is as good or better than what I can easily buy.
Reply With Quote
  #4  
Old 28-03-10, 09:54 PM
DLH's Avatar
DLH DLH is offline
Senior Member
 
Join Date: Dec 2004
Location: Detroit
Posts: 123
Default

Yes species matters but as with all things its not that simple. Different varieties of the same family may have greatly different shrinkage characteristics. For instance, Bigleaf Maple has a tangential shrinkage rate of 7.1% placing it in the middle of the pack. Silver Maple on the other hand has a tangential rate of 9.9% considerably higher than average. The same species grown in different places my have different rates. Douglas fir grown in the west coast has a tangential rate of 7.6% but when grown in the interior its 6.9%. Old growth Douglas fir has different rates than new growth. When purchasing lumber the dealer may not know exactly which species he is selling or where it is grown. He may tell you what he thinks you want to hear.

As we have noted, Wood moves at different rates in tangential and radial directions. In general, the larger the ratio between tangential and radial movement the greater the species tendency to warp.

As David mentioned in another thread, how the board is cut affects its stability. He pointed out the superiority of quatersawn, (also called vertical grain) wood. Here is an image that demonstrates the point. I found it at, http://www.woodworkdetails.com/Knowl.../Movement.aspx



It shows the various cuts from a tree section and the likely size and shape of a board or pole cut from it. The quartersawn sample is on the lower left. Note that the one in the center also exhibits mostly vertical grain but it should be avoided. This cut is called boxed heart. While the edges have vertical grain the center is mostly tangential. The stresses in the transition often cause cracking as it dries.

This article has a fairly comprehensive chart showing shrinkage rates of various species: http://tnvalleywoodclub.org/Articles/Wood_Move.htm

Here is a wood movement calculator: http://www.woodworkerssource.com/movement.php

Art history is not necessarily a good guide in selecting wood for panels. In Renaissance Italy panels were usually made with more or less stable materials, while in northern Europe Oak was popular. While admittedly strong many varieties have high shrinkage rates and high tangential/radial ratios. Painters simply used what was at hand.

Weight and strength are also factors in choosing wood for panels. Id pass on the Oaks, Maples and Ashes on weight grounds. Redwood and Cedar are light and stable but may be a bit too soft. My choices for solid wood are Poplar and Basswood. Poplar has a lower overall shrinkage rate but Basswood has a lower tangential/radial shrinkage ratio, making it a less likely to warp. Both are light for hardwoods. For plywood I am less concerned. As I said, the cabinet grade plywood I use, (usually leftover from cabinet jobs) often has a poplar core. I use a lot of Lauan plywood. It is widely available and fairly cheap. By a wide margin, both in solid wood and plywood my favorite is Mahogany. It tops the charts for low shrinkage, stability, workability and beauty.
Reply With Quote
  #5  
Old 29-03-10, 02:39 PM
dbclemons dbclemons is offline
Senior Member
 
Join Date: Mar 2006
Location: Texas
Posts: 227
Default

Thanks, Doug. That further emphasizes my point on how important it is to select the right type of wood. For example, if you buy a birch panel, what kind of birch is it, paper, yellow, river, Mongolian...? As you mention, you'll wind up having to trust your source.

Here are a few more links to toss out:

That graphic above comes from the USDA Forestry Service, and you can read their article here regarding moisture effects on wood:
http://www.fpl.fs.fed.us/documnts/fp...tr113/ch03.pdf
or browse their site for more info:
http://www.fpl.fs.fed.us/products/pu...ions/index.php

The density of the wood affects it's weight. MDF has density roughly 30-50 lb/cu ft. HDF is 50-80. The density of solid woods varies greatly. In the case of plywood the weight is mostly a matter of what type of wood makes up its core. Yellow poplar or pine have a density @ 20-30 lb/cu ft. and are most commonly used.
http://www.engineeringtoolbox.com/wo...sity-d_40.html

Density and resin content also effect how well the wood will accept paint, glues, or stains, which along with its shrinkage ratio is very important for artists to know. This Wood Explorer site has a good databse of wood properties:
http://www.thewoodexplorer.com/
Reply With Quote
  #6  
Old 29-03-10, 09:06 PM
Koo Schadler's Avatar
Koo Schadler Koo Schadler is offline
Tempera Painter
 
Join Date: Dec 2003
Location: Alstead, NH & Zirahuen, Mexico
Posts: 299
Default

Given that you guys are so knowledgeable about these supports, I have some questions...

1. What are the practical differences between MDF and HDF, aside from the fact that the first is of medium density, and the latter higher density?

2. Why are HDFs more prone to curling, as you mention David?

3. Where do you all come down on the tempered versus untempered hardboard debate?

4. And finally, while I agree that hardwood plywood is a better support than fiberboard, I wonder if you have an opinion as to how much better. Another way to ask this is: if a good quality, untempered HDF support is prepared well and coated with true gesso on all sides, would you all consider it a fairly archival support - or would a good quality plywood be significantly better?

Thanks,

Koo

Last edited by Koo Schadler; 29-03-10 at 09:08 PM.
Reply With Quote
  #7  
Old 30-03-10, 01:31 PM
dbclemons dbclemons is offline
Senior Member
 
Join Date: Mar 2006
Location: Texas
Posts: 227
Default

There are various mills that make both and they follow no real standard. The big deal with them is that they are designed mainly for construction purposes, not art use. They don't say what's in them only what isn't for environmental reasons.

1. MDF is available in thicker widths than HDF that gives it more stability. I've never seen MDF thinner than 3/8". MDF is not tempered. I don't know of any MDF that's made from hardwood, but some HDF is made with aspen, as Ampersand and Real Gesso declare that for their HDF panels. The same width MDF would be cheaper. Some HDF is smooth on only one side, MDF is always smooth on front & back.

2. Both will curl or twist. That's what wood does. Curling of MDF is less pronounced if it's thicker.

3. The amount of oil used for tempering HDF is very small, although it wasn't always that way. Linseed is common, but it could also be tung oil. It's purpose is to help prevent moisture penetration and add strength. If the board is properly sized it doesn't much matter, but untempered is a safe choice, when you can find it.

4. While I have painted directly on prepared HDF panels, and may still on occasion, the main reason I prefer plywood is that I know what I'm getting and how that will behave. There are no guarantees on longevity. You can compensate for the shortcomings of composite panels by using them as a support, gluing veneer, canvas, or paper to it instead of painting on them directly.

P.S. Recently I've been testing out a new wood panel product called "Extira." It's similar to MDF but is made with 100% hardwoods. So far the results look promising.
http://www.extira.com/
Reply With Quote
  #8  
Old 30-03-10, 01:43 PM
Paul B Paul B is offline
Member
 
Join Date: Feb 2008
Location: Norfolk England
Posts: 32
Default

Thank you for your answers. I really apreciate all the time you have taken to answer this thread. I am really grateful. There was so much useful information in there.

Does any one know if aliphatic resin glue e.g Titebond is a good glue to use. Is there a problem with out-gassing with it. I have used it for making a musical instrument and would feel very confident with it in terms of strenght etc. Also if each piece of wood is well cut and smooth the amount of glue that is left inside a joint after clamping is tiny. If I buy ready made plywood could there be a problem with out-gassing? I suspect outgassing is not a problem with glues?

Is there a minimum thickness of veneer that must be used for the outermost veneer? or does 'cabinet grade' ensure a certain thickness. I googled plywood but the companys I found did not state the thickness of the outer layer or glue used. I could email them if I knew what I was looking for. I would have thought peeling could be an issue if the outer layer is thin?

The wood I used recently and had trouble with was solid oak 2cm thick. Although one panel was only 24cm largest dimension. I was supprised when I found I could actually bend the panel just using my hands, and each layer of gesso had to be the same front and back to keep it flat. I realise ply is much more ridged.

I started to type in this question but then deleated it once in case it was to stupid, but is there a term for a thin piece of wood thicker than a piece of veneer or can veneer be 5mm thick in theory?

Thank you once again for all the great info given so far.
Reply With Quote
  #9  
Old 30-03-10, 04:11 PM
MatG MatG is offline
Member
 
Join Date: Dec 2008
Location: Four Corners area, AZ
Posts: 64
Default Linen and canvas over plywood

After working with a maple veneer panel that I prepared myself with traditional RSG gesso, I had problems with the grain appearing through the paint surface. It looks like tiny horizontal cracks.

My understanding was that any wood panel should have a linen or canvas surface applied over it with additional gesso. The posts here imply that you are painting directly onto a gessoed surface applied only to the plywood panel.

Is linen (or canvas) laminated to the panel surface required or is it optional? What are the merits of each?

For what it's worth, I've been using True Gesso panels, and I find them to be high quality. They do not at all seem cheap, and I wouldn't worry about pricing high if the painting warranted it.
Reply With Quote
  #10  
Old 30-03-10, 04:53 PM
JeffG's Avatar
JeffG JeffG is offline
Administrator
 
Join Date: Jan 1970
Location: US (NJ)
Posts: 121
Default

Quote:
Originally Posted by MatG View Post
...Is linen (or canvas) laminated to the panel surface required or is it optional? What are the merits of each?
Matt, I'm glad you asked this because I wonder about it too. I assumed that the tradition of gluing linen or muslin to a wood surface and then gessoing on that was to keep micro-cracks from developing if the wood surface moved on its grain. Also, I'd think that the linen/muslin substrate would help one remove the painting from the wood backing if the panel somehow became compromised.

I am hoping to experiment with making and using aluminum panels that will be primed with RSG gesso, probably with a fabric layer (linen, muslin or polyester) between the aluminum and the gesso. Who knows when I will get around to this, but I'll keep you all posted, and would appreciate anyone's feedback on this idea.
__________________
Jeff G
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 09:29 PM.
Design modifications, graphics and CSS by RobM
June 2010



Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.