MITRA Forum Question Details

​​​Thanks for asking this Ron​.​

​i understand what you mean, but not a good practice as acrylic is porous, so it doesnt block penetration at all. consider using polyester as your canvas, as it is inert to RH change. 

​Fellow artist's opinion.  It seems like something ​that's wrong, but I can find little logically against it.  Sizing the back solely with acrylic medium is sometimes advised against as the dried acrylic gell remains open to absoption of dirt, but one would think this less of a risk with acrylic gesso. ​The gesso is mildly porous to moisture, but stops rapid water absorption.  As it's not a complete blocker, it has less risk of creating a hidden unwanted hermetic mirco environment of mold.​​

Restorers would however likely resent its presence when repairing canvas tears as its an intervening layer to the broken fibers.  Reweaving would be almost impossible (though this is rarely done anyway with most canvases) edge gluing perhaps?  Or with a lop sided smile, just bridge layer strand fibers over the top as though the gesso isn't there.

As to stiffening I suppose the orthodox view would be to just put more layers on the right side.

Marc Kingsland.

Hello there Ron,

I'm aware of some trends of varnishing the reverse side of the canvas to protect it from mould. That has fallen out of fashion a long time ago, but I doubt there's much to fear from that. To an extreme degree of the logic, you could technically prime, paint and varnish both sides of your canvas cloth after all.

An acrylic sizing won't absorb and retain humidity as much as a rabbit skin glue sizing (which does relax a lot). 

However acrylic gessos keep a porous surface which lets ambiant humidity pass through. Meaning the surface still breathes slightly, and can still rot in excessive humidity.

But if you want stiff "drum style" canvas, rabbit skin glue will be more efficient than the soft and souple acrylics for your sizing.

So if you want something drum style and tight, I'd advise rabbit skin glue gesso and varnish the back on a day when the air is dry.

Otherwise pure acrylic over mixed fibres cloth will surely breath less depending on humidity (can still develop some mould nonetheless), but I'd have other concerns for the longevity of plastic fibres and long terme adhesion of coats over it. (low van der walls adhesion, no porosity for the "sizing" or gesso to anchor itself either. It's painting on plastics literally)

Avoid the mistake of putting an acrylic gesso over a rabbit skin glue sizing. Further stress from "breathing" or retractation of next paintings can delaminate the acrylic rather easily and cleanly. Oil ground over rabbit skin glue is more advised.

Good luck.

Lussh