MITRA Forum Question Details

We are very happy that you find the site useful. It is true that the conservation field would like to persuade artists from using RSG because of all of the issues you are well aware of. I also understand the reluctance of some artists to abandon this material due to the qualities it imparts to stretched canvases.

So let’s ignore those issues for the moment and focus on the suitability of using animal glue to adhere a finished painting to a rigid support. First, as you suggest, it is far preferable to adhere the canvas to the support before painting. You know this as well, so let’s move on. In the situation you outline, I would strongly suggest that you use an acrylic dispersion medium or gel in place of the RSG. It is less likely to cause issues in the canvas while drying and creates a far better bond. Animal glues are very strong and have great adhesiveness but are poor gap fillers. When gluing canvas to a rigid surface, it is generally far better to use an adhesive that good cohesion and fills the interstices of the reverse of the fabric rather than an adhesive that has amazing adhesive strength but is a poor gap filler. We do cover this subject to some degree in our RESOURCES section under Rigid Supports.

When possible, it is preferable to avoid introducing moisture to a completed painting or one that contains an animal glue size. Water added at this point may cause uneven buckling. This is not always possible and is one of the reasons why it is best to completely prepare the canvas/panel substrate before painting. You could possibly use a thermoplastic heat-activated adhesive like BEVA 371 as well but that would depend on the surface texture of your painting and the degree of impasto. I also suggest that you allow the painting to dry for some time before even thinking about applying heat to the surface. Again, you can read more about this in our Rigid Supports PDF.

​To be perfectly clear from the begining, this procedure is not optimal, as you already mentioned.

I think that the answer to your questions is yes. Just to be sure we are on the same page, I would not suggest sizing the hardboard panel with animal skin glue and then use acrylic dispersion medium for adhering canvas. This may cause problems as well and there would be possible incompatibility (or at least solubility and dry time problems and issues). In place of this you could size each size of the panel with the acrylic dispersion medium and then adhere the rsg sized primed and painted canvas to this panel using the acrylic dispersion medium. Done carefully, this should work fine, or certainly as well or better than the using rsg to glue the canvas.

On the final though, varnish will likely slow down the penetration of moisture into the stratigraphy but it would not really stop it. If this were the case, the hygroscopic nature of animal glue would be not issue at all when used on panel paintings. A final word of caution, though. Care needs to be taken to restrict unrestrained movement of the canvas (weighing, etc) to prevent any subsequent shrinking during the process (this is why we always suggest adhering the canvas to panel before painting) to prevent damage to the ground and painted surface.

​We would not advise going this route however we are also not 100% positive that it wouldnt be fine in the long run either (as long as you document what you choose to use on the back). One concern would be that in places where the acrylic has seeped through the canvas weave, the RSG might not adhere well to these areas. Conversely, the canvas could also become less absorbent overall, therefore making your RSG layer function more like a coating (which is more problematic) rather than a size layer.