ristin DeGhetaldi, I am researching sizing of canvas for stretched supports. I have tried both Gamblin PVA and GAC100 for preventing the leaching of oil to the canvas, to prevent rotting. I prefer using the Gamblin PVA, because it seems to soak into the canvas better, and therefore is easier to use (also, it is less cost prohibitive). However, I am still concerned about too much flexibility with either of these PVA sizings when used with acrylic gesso and stretched canvas. The fully cured oil paint will be more rigid than its substrate, which could lead to cracking, long term. To do it better, and get more compatible flexibility, I am thinking that adding GAC 400 might be a good option. This would make the substrate stiffer and of similar rigidity to the fully cured oil paint. Am I right here?
If so, what would be the best order of operation? I am guessing a layer of Gamblin PVA on the front then back, before stretching, then a layer of GAC 400 on the front, after stretching. Then I would wait a day before gessoing twice with high quality acrylic Gesso, like Golden. Then, I would wait 3 or 4 days before painting. I would appreciate your opinion. Thanks!
Thanks, Sarah! I did read your suggested link. The quality of information was fantastic. I have some questions. If I size with GAC200, two coats, how long would I have to leave the heating at 72 degrees for proper curing? How long between coats? How many coats of Golden Acrylic Gesso would be ideal for glazing? I have noticed that a medium openness is ideal for holding a glaze. What would be the ideal procedure for mounting canvas to panel? Thanks so very much.
I have learned that there is no sizing on virtually any premanufactured canvases in Canada to prevent the oil from doing damage. This has spawned my research. If any one knows of manufacturers that properly size their canvas before gessoing, please share this information with us all.
Hi Kathy! Happy to help further. The GAC 200 only needs to dry while at 70F, so once it appears clear and not cool or clammy to the touch, you are fine. Could easily be a matter of a few hours. As for time between coats, again, once clear and touch dry, you are good to go. The first coat usually dries very quickly because of the absorbency of the canvas, so I could see doing the second coat 1-2 hrs after the first, and then letting that sit for another 3-4 hours to be safe before turning down the heat. As for the ideal number of coats of acrylic gesso for glazing….great question and would think it might vary depending on each person’s taste. I would start at 2 coats as that will still hold onto the texture of the canvas, and then if you want something smoother, add a third. And finally, for mounting canvas to panel, you have several options. Having a canvas removable for conservation purposes is always best, so if willing to explore the use of BEVA, which is a heat activated adhesive used frequently in conservation, you can purchase that as a brush-on gel or as a film. We purchase ours from Talas, which you can find at Talasonline.com (put BEVA in their search box)and you should also read the Resource Page for Adhesives and Sizes that you can find here https://www.artcons.udel.edu/mitra/resources as that has a section on BEVA and even its use for mounting canvas to panel. If not concerned with reversibility, you can certainly use an acrylic gel or medium as an adhesive. You can see a short video where we show the use of Soft Gel for adhering paper to a panel, but the process for canvas would be similar: https://www.youtube.com/watch?v=ggB1veQmwNU&t=1s One concern I would have in either of these cases is that tyou would be working with a finished painting, rather than simply adhering unpainted canvas to a panel, and so there might be risks to damage or deformation of texture in the painting from any application of pressure and heat, so hopefully one of the conservators might be able to chime in with a best practice in that case.
Hi there….I am sure one of our moderators who is familiar with GAC products will respond soon. But in the meantime feel free to consult our documents in the Resources section….particularly the “Flexible Supports” regarding stretching techniques and “Adhesives and Sizes” as well (do not forget to scroll down to the bottom of the last document as there are many helpful links there).
Hi – The first thing I want to point out is that GAC 400 only works if applied directly to raw natural fibers and so should NEVER be applied to a canvas after already sizing it with PVA or any other material. The reason is that GAC 400 is not meant to be used as a continuous film, where it would prove to be too brittle, but really as a thin penetrating coating of the fibers that stiffens them. Also, if the GAC 100 feels too thick or is not penetrating into the canvas enough, it can be thinned with some water (up to 1:1), but then of course the resulting film will be thinner and multiple coats might be needed to get the same amount of oil blocking. In terms of using acrylic sizes for preparing canvasses, I would recommend reading through the following article where we summarizes a lot of the testing we did using different combinations of materials and looking at how stiff and effective at oil blocking they were. These tests included PVA size and Rabbit Skin Glue, so were not restricted to acrylic alone: http://www.justpaint.org/preparing-a-canvas-for-oil-painting/ In terms of stiffness, you are correct that the stiffer you can make the canvas the better, and that using GAC 400 is definitely helpful. in this regard. And, as you will see in the above article, if you have a studio or workspace where the temperature is reliably at 70F or above, another option is simply to skip the GAC 400/GAC 100 combination and use just two coats of GAC 200 followed by either an acrylic gesso or an oil ground. And finally, if able to coat the canvas prior to stretching, another ideal system would be to use GAC 400 on the back side, stretch, then apply a coat of GAC 400 to the front, and then simply apply 3 coats of acrylic gesso as we know 3 coats of a high quality one will block oil penetration and would be stiffer than, say, GAC 100 followed by a couple of coats. Finally, keep in mind that the canvas will remain the most flexible material in the system, even after all of these steps, so using a panel will always be the most stable option, or when possible, mounting the canvas to a panel afterwards.
Hi to answer your first comment….Sarah can answer with more specifics regarding sizing using acrylic gesso for glazing. Information regarding how to adhere your canvas to a rigid support, please refer to our “Rigid Supports” document as there are instructions outlining various procedures for doing so. As for your second comment there may well be a few brands of commercially available canvas that are sized (it is difficult to confirm this without analytical testing and/or obtaining confirmation from a manufacturer), but it sounds as if for the most part the many brands you have tested have not been to your liking in terms of being able to prevent “strike-through.” We will reach out to a couple industry reps who sell commercially primed canvases who may be able to provide you with additional information regarding this topic….it may also be that you could purchase a higher quality commercially pre-primed canvas and simply apply an additional layer of acrylic dispersion ground (“gesso”) as well.
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