MITRA Forum Question Details

Hi Eli,

My paintings are fairly small, I'm not experienced with large panels - so, unfortunately I cant be much help. Here are a few thoughts that may or may not be relevant to your situation.  

Given the many variables (glue bloom strength, concentration, number & thickness of layers, etc.) I would think it pretty difficult to calculate the force of gesso.  Even if you could, the unpredictability of RH absorption can still leave a wood-based panel open to movement.  Small panels also warp if the coating on the two planar sides are too disparate. 

What I've found the most helpful to reducing warp is to make sure both front and back have equal numbers of gesso layers.   I recognize you can't achieve that if a panel is cradled (frankly, as I believe we've discussed here before, I think cradles both solve and create problems in a panel).  Are you willing to work with plywood?  If you were to use ½" thick minimum (¾ to 1" would be much better, albeit heavier); apply cloth to both planar sides; then apply an equal number of gesso layers on both sides; coat the back with house paint; apply ET paint to the front - in my experience that's a pretty stable panel. 

Another option is honeycomb aluminum.  If you were to attach cloth to the front using BEVA or a PVA glue (use a tight weave, so the glue doesn't travel to the face of the cloth, which could affect gesso adhesion), traditional gesso would adhere to the fabric.  I've tried it; it's a light weight, stable option - however not having a wood-based support does decrease the absorbency of the painting surface, even with traditional gesso; the water in the paint runs into the aluminum, so it stays more present in the gesso/paint layers, which makes everything slower to dry.  So if you have watery working methods, ET won't behave the same on aluminum; however, if you work drybrush, it behaves pretty well.

I'm not sure about the answer to your second question.  What I can say is that the water in gesso evaporates out, leaving behind the same ratio of binder to pigment as when you started - so adding more water doesn't weaken the glue, per se; it would make for thinner layers, so in that sense they would be less strong (but also less thick, and hence less absorbent).  Also be aware that adding a lot of water can make the binder (glue) so attenuated that the solid particles (chalk, gypsum) are somewhat under bound. 

If you figure something out, please let us know - I'd be interested.

Koo

​Even if a cradle is wood-free, as long as the panel itself is wood-based it will want to move - and if it's attached to a cradle that doesn't move, than that disparity creates tension and will create cracks in the gesso.  

There are complicated cradle constructions that attach to a wood panel, but only loosely, so the panel can still move a bit in response to RH, but not flex - I have one (made by a company called Studio Products, many years ago); it's quite complicated, worked only moderately well (came unglued in parts).  Still, that sort of cradle is an option, albeit labor intensive.  See this link:  https://en.wikipedia.org/wiki/Cradling_%28paintings%29

I don't know where to get honeycomb - I got a sample by calling an aluminum sales rep, many years ago.  Have you tried contacting signmakers?

You are correct, traditional gesso doesn't adhere well to synthetic polymers (such as PVA glue).   So you would have to be very careful to have enough glue on both the panel face and fabric back so that every inch adheres; yet not so much glue that it soaks through to the fabric face.  It would be tricky, as you really do want good, consistent adhesion between every inch of the fabric and panel.  

You'll often hear BEVA film recommended as an adhesive for aluminum and fabric, but in my experiments I found one needs to get the exact right heat setting, or the BEVA won't adhere properly - using an iron definitely didn't cut it. In my estimation you need to use a temperature control dry mount press to get the BEVA to properly, consistently activate and adhere. 

​Panels can have amazing memories - I'm glad your panel is flat again, but be aware it may or may not stay that way, once fluctuating RH enters into the picture.  Good luck and keep us apprised. 

Koo

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​Thanks for the update, Eli. I've had panels that warped (due to ueven coatings on back and front) that I tried to amend by remoistening the wood, then applying weights to flatten it (it did flatten), then applying additional coats to the convex size to even the tension, then reapplying weights to encourage the panel to stay flat...only to find that, after all that effort, on a humid day the wood bent once again!  So yes, wood has a very good memory.  I don't think a panel will necessarily curve much, if any, beyond the original bend, nor grow new convexities - but with the slightest encouragement (humidity) it will want to return to that original bend.  I'll be interested to hear if your framer's fix works longterm; frankly, I'm doubtful.

My experience is that ¾" plywood is pretty stable, not quite but nearly as good as 1".  I'm still dubious about applying wood based panels to an aluminum cradle - hardboards too swell and change dimensions with humidity, and if it can't do so (being attached to an unmoving base of aluminum) those tensions will travel into the gesso and paint layers.  It may cause cracks (hairline generally, to start) quickly, or they may take years/decades to appear, but I think the difference in the two materials will at some point have consequences. 

​Sigh....let us know how it goes.  Koo

​Hi Eli,

This is great information - what a good idea to screw and/or clamp the boards while gessoing, and I appreciate you measuring the bend in the boards to clarify the effectiveness of the method.  If I ever get around to doing an update of my Egg Tempera book (which I hope to; there's so much more to say!) I'll include this information, for sure.  Thanks for reporting back to us.  

Koo