The best practice in prepping a stretched canvas for oil paintApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2016-11-10 09:43:46 ...
Most recent comment 2016-11-10 11:59:00
Art Conservation Topics
Sizes and Adhesives
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!
Answers and Comments
EditDeleteModerator AnswerHi 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).
EditDeleteModerator AnswerHi -
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.
EditDeleteModerator AnswerHi 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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