MITRA Forum Question Details

​Hi Brian and others, Thank you for your detailed responses and I apologize for not reviewing the forum and resources first. I did not understand that I could search the content by keyword but now I do and have!

Thank you for confirming that tempered hardboard is not only OK but superior to untempered (standard). I read the Ampersand link and was reminded that before I started my previous 4' x 8' panel I had communicated with them about obtaining one of their panels in that size. It turned out that the price of shipping was prohibitive. I also inquired about buying similar panels but could only purchase them in quantities of 100 which would be impossible to store and require several lifetimes to create paintings at my slow painting pace.

I do carefully cradle my hardboard panels right up to  the edges and champfer the edges prior as Koo recommends. I have been using kiln-dried douglas fir, which although it is technically a soft wood has a very high hardness rating similar to hardwoods. However, based on your resources section I will look for kiln dried oak or maple. I found it curious that in the rigid panel resource section is states that only the bracing on the edges is to be glued. The interior braces should be affixed to the outer bracing using hardware. I assume that is to allow expansion and contraction of the wood, similar to the cradling used on panels constructed from planks of wood (at least the ones on very old paintings.) But perhaps this is unnecessary and I can continue to glue my bracing to the interior of the panel as well as the exterior?

Getting back to type of panel, I looked into 1/8" plywood (as I am currently using 1/8" hardboard due to weight considerations in a 4' x8' panel). It seems it may be difficult to source high grade 1/8" plywood as most of the airplane grade plywood only comes in smaller sizes. Perhaps you have a source you could share? "Baltic Birch" seems recommended but only comes as large as 5'x5' . Plus in your resource section it recommends maple, walnut or mahogony and not birch as birch may cause more checking. Finally, even if I find a source, due to size, panels are usually shipped by freight which is very expensive. But if I do find a superior panel for my purpose I would be willing to pay in the hundreds but maybe not in the thousands for one panel!!

So I may need to stay with what I have recently used which is 1/8" hardboard, made from Douglas Fir (which is abundant in the NorthWest.) It is manufactured in Oregon and distributed by the Stimson Company. If I could find a source for 1/8" high grade hardwood plywood, I would then apply a muslim layer as you suggest. And from what I read it would be lighter than the hardboard which would be a real plus.

I am wondering if aluminum is lighter than hardboard and/or plywood, but at 4'x8' would probably still need bracing, which would add to the weight, and I don't know if hardwood strips would adhere or if metal bracing would be required?

Best of all, your recommendation that I would NOT need to apply  8 coats of gesso to the rear and could just use the semi-gloss alkyd paint, since I do a pretty good job of bracing. That would make the painting a great deal lighter. Thanks for the link to Koo's question- that helped. 

BTW, what do you think of the Joseph Edward Southhall substrate for ET? He (or I believe his wife prepared his panels) stretched a loose weave canvas to a wooden frame and then applied equal coats of gesso on either side. The gesso adhered through the loose weave. It seems precarious to me but his paintings seem to hold up with the test of time.

Thanks so much for this extraordinary forum!!

Lora

Hello Lora and Brian,

A few thoughts and questions to add to the conversation. My understanding is the idea of oil migrating up to the surface of a tempered hardboard panel isn't accurate; the oils within tempered hardboard are drying oils, they cure and can't travel within a panel. The presumed problem with a tempered board is more that the oil content makes the surface slightly less absorbent, and thus the gesso doesn't "sink in" and adhere quite as well as on an untempered material.  Still, it adheres well enough, and there is the benefit of greater strength.  So, an untempered board isn't as strong but allows for maximum mechanical adhesion (in my experience, mechanical adhesion is very helpful to long term durability); however a tempered board is a stronger panel (also very important) but with slightly less optimal adhesion.  Is all that correct, Brian?

I know there are manufacturers who have more experience with ACM (aluminum composite material) panels than I, and hopefully they'll chime in.  For now, here's a bit about my experience.

I did the cross hatch adhesion test (as outlined by Golden on their website) of traditional gesso atop an ACM panel and had a pretty high failure rate (see photo). KS - Cross Hatch Adhesion TG to ACM.jpeg Attaching fabric first to the surface made a big difference. 

Regarding how to attach fabric, BEVA is often mentioned as a good option and conservators tend to favor it. However as a practicing artist, it's a bit complicated. The liquid form is quite toxic, I don't want to work with it.  BEVA film takes care of the toxicity, but my experience is that to create a good bond, the temperature needs to be very carefully calibrated, which is hard to do with an iron; air bubbles or imperfect adhesion can result when the temperature is off.  I had my framer use a heat vacuum press to adhere some sheets, which worked better, but that limits the size and adds costs.  Are PVAs and acrylic gels considered durable (albeit irreversible) alternatives for adhering fabric to aluminum?

I've done maybe half a dozen tempera paintings on ACM at this point, and the results are good but with a few caveats.  First, the drying time of both the gesso (as it's applied) and egg tempera paint is different from on top of wood based supports; in fact, substantially different if the applied layers has lots of water in it (like a thinned glaze or petit lac) - I experienced up to 10 times slower drying times for certain tempera layers atop aluminum. This make sense; the great benefit and drawback of wood based supports is that they act like a sponge.  So if you work with watery paint and/or in a humid climate, expect slower (potentially much slower) drying times (as well as, potentially, more lifting of underlying paint layers as a consequence).

A hairdryer can help speed things along, but be careful – it can also, if used too often (even on moderate heat), warp an ACM panel (I presume because it's affecting the interior plastic core).

Finally, ACM panels can definitely develop a bow in them; I had it occur even in a very small panel just from the number of layers of gesso and paint on the front.  And, although rigid, the panels are thin enough that they flex, especially at large sizes, which would be hard on traditional gesso and egg tempera, particularly as ET ages.  I think bracing for large panels is a good idea, although I'm not sure the best way to do this.  

Kudos to Lora for working on such large scale temperas - most ET painters work relativley small, but you and Botticelli (among others) show us an alternative. 

Koo