MITRA Forum Question Details

There are concrete issues associated with the use of animal glue as a sizing. A search here will should reveal a number of threads on the subject. You should also read through our downloadable PDF on adhesives and sizes in our Resources section

https://www.artcons.udel.edu/mitra/resources

There is certainly an advantage in preshrinking the linen. There was a time when the most fastidious would shrink and stretch the linen many times until much of its reactivity was thought to be removed. In practice this was not really possible (the fibers will always absorb water and swell causing some shrinkage) but certainly the linen did have a tighter weave. I would not do this unrestrained in a washing machine, It would be far better to attach it to a temporary strainer and wet the linen. After it dies you could then restretch until you are satisfied. Whether this is worth it to you is another question. Also, it is not essential that all fibers be encapsulated by a size but just those in contact with the oil primer, if such is being used.

Despite the inherent issues and my being a painting conservator who is aware of the possible problems with animal glue, I always use animal glue when sizing linen for oil painting BUT ONLY WHEN USING AN OIL PRIMER. It is nonsensical to use animal glue under an acrylic dispersion ground. I just love the stiffness it provides and appreciate the way in when the linen can be gently sanded after the first coat dried to remove the fuzz from the surface. I would also suggest that linen always performs best when it is over a rigid support rather than a strainer and stretcher but that is a separate issue and one that has been covered many time here on MITRA (please do a search). Multiple coats of acrylic dispersion or PVA medium sizes are very much superior in terms or reactivity to changes in relative humidity. Again, this has been covered many times here on MITRA. Much of what perceived as the virtues of animal glue is the resultant stiffness of the fabric. It has been shown that the same stiffness can be achieved but the application of multiple layers of acrylic dispersion ground to the fabric.

Finally, and I make no claim to the superiority of the following, but this is the procedure that I used when I was using animal glue to size fabric, preferably when stretched over a rigid support: I would apply 2 to 3 coats of size depending on the weight and weave of the canvas. The size coats were rather thin. It i difficult to talk about how much glue to water since each brand likely has a different "bloom strength" The glue that I used worked best with about 6 level TB glue soaked and dissolved in a quart of water using a double boiler. I would gently sand the canvas to remove fuzz and any slub protrusions after the 1st coat had completely dies and again after the 2nd if I intended to use 3 coats. I never sanded the final coat.

You could also use large stretcher frames to create temporary stretching & priming frames, similar to Vellum/skin drying racks or medieval embroidery frames. By attaching the canvas to the stretcher frames with threads, you can quickly readjust the tension, so if you brush on water first to wash the canvas and it goes slack, you can just pull the threads tighter. But as Brian said, and particularly because your linen canvas appears to be of poor quality, your paintings should hold up longer if you adhere the linen to a panel to give extra support. The center of a large scale canvas usually moves more and bounces back and forth any time the painting is handled. This could exacerbate cracking and flacking issues of RSG & oil primed canvases. For large paintings polyester cloth is a great choice as it is the most inert of all the fabric supports and it can be stretched very tight without slackening.   ​​