MITRA Forum Question Details

Hi Eli,

Wood-based panel are porous and absorbent.  In the days before engineered panels (fiberboards & plywood), when all panels were solid wood, applying cloth atop a panel was an important step to prevent wood grain from telegraphing through, and to minimize inevitable movement in a wood panel.  If cloth is soaked in glue, then applied directly atop a wood panel that has not been primed with glue, the absorbent wood soaks up the cloth's glue, and this decreases adhesion - you can get pockets of unattached cloth.  So it's important to cut the absorbency in a wood panel with a layer of glue; then apply glue-soaked cloth on top. This way, the glue in the cloth doesn't sink in and disappear into the porous wood but instead adheres to the glue layer atop the panel.  

This step is especially important when applying cloth to a panel because cloth and wood are very different materials, and you want to maximize adhesion between them.  I would say it's slightly less critical to apply a layer of glue atop a fiberboard panel that is not getting a layer of cloth (not necessary since fiberboards have no wood grain), but instead is having gesso applied directly to the board (becuase warm, liquid gesso sinks in and attaches to fiberboard better than cloth).  Still, I think it's preferable to first apply glue to fiberboard, to cut absorbency, let it cure overnight, then apply gesso.  The pure glue layer sinks into fiberboard better then gesso (given its solid particle content); the warmth/moisture of gesso rehydrates the glue layer so that the glue layer and gesso grab onto one another.  Better adhesion amongst all the layers, it seems to me.

Animal glue will not block moisture, it attracts moisture.  The porosity/hygroscopic nature of wood-based panels, animal glue and traditional gesso are what give ET painters ideal control of the medium (because the water in the paint gets whisked away, doesn't sit on the surface & create lifting).  That porosity also provides "storage" for non-drying, mobile lipids in egg yolk (conservator Alan Phenix told me he saw more "Fatty Acid Migration" in ET painted on a nonabsorbent support [mylar] then he did on wood based panels).  All that's the good news about the porosity/hygroscopic nature of wood-based panels, animal glue & traditional gesso.  The bad news is that these materials attract relative humidity, which can cause problems as a painting ages.  There is no getting around the conundrum: the porous, water-loving nature of ET's traditional support and ground is both a benefit and a drawback.  ​

And I appreciate your enthusiasm and curiosity for the craft of painting - you ask good, clarifying questions.   Cheers in return.    ​​