Preservation of canvas

​Are you finding that you are getting oil stains around areas of paint? Or can you not tell because you are covering the entire canvas with oil paint?

Without applying something to isolate the fabric from the paint, I don’t think cotton muslin is a good choice for this approach, if durable results are the goal. Since polyester artist’s canvas is not susceptible to the destructive effects of direct contact with drying oil, and since you mention you are already using both poly and muslin, synthetic seems the better choice. I would recommend using a bona fide artist’s canvas rather than something from the fabric store, which may have surface treatments, unstable colorants and optical brighteners. 

I would also be interested to know the planned display/installation method. Will the fabric be stretched, mounted to panel or suspended freely? That will be important as well.

Thanks for the additional detail. It sounds like you are selecting a light, po​rous fabric to deliberately induce strike-through of the paint. I would expect cotton muslin to become saturated with the oil paint vehicle, which can have a destructive effect on the fabric. There is a precedent for painting on thin muslin, in historical stage scenery backdrops, but obviously those would not have been expected to have survived into antique age (and I believe casein was often the medium used, for fast rate of drying and matte finish).
Another issue with the application of oil paint (even in stick form) to an unprotected, absorbent support is that enough of the paint binder can be taken up by the support material to leave the paint layer under-bound. 
In my opinion, the most significant challenge with the approach you describe is the vulnerability of the aging paint film on a support material that may not resist deformation from gravity and other forces that will cause the paint to move and flex. Canvas that is considered heavy enough for use as a painting support would not normally be thin and porous, because it needs to provide a flat plane with minimal movement. Based on these factors, I think this project would be better suited to acrylic paint, a medium that will maintain strength and flexibility for a long time. 
I would be interested to hear from the Moderators who are qualified to speak to conservation issues- I would expect a thin, porous painting with color on the verso would present unique conservation challenges.

Sorry for the belated response. I was away for a couple of days. I will reach out to one of our moderators more experience with oil sticks to weigh in on this.
As to my thoughts, I need to sort of separate my role as a conservator from that of a moderator here. As a conservator, I need to approach all paintings as the artist intended and honor their choice of materials as a component of their aesthetic and process. This is different from the goal here, which is to offer as much information about the options available to arm the artist with the knowledge to make informed decisions on their materials choice and methods beforehand.
 So with that stated, I have to agree with Matthew on all of the points that he raises. Supports generally perform best when they either possess inherent rigidity that is greater than that of all layers that will be added (you do need to take into account the aging properties of the added layers…will they become more brittle with time?) OR supports that are made rigid through the application(s) of size and/or ground layers.
Your process sort of sidesteps these criteria. The open weave and extremely insubstantial nature of muslin is unlikely to adequately support the oil stick application as it ages. Your lack of ground means that the fabric is not made more rigid that in its untreated form.
The above also ignores the issue of oil absorption into the cellulose fabric. We have written about this on MITRA in the past. There is some danger of this rotting the fabric overtime. The lack of oil staining may mitigate this potential problem but it does not mitigate the issues above.
So, taking Matthews comments and these into account, it would probably be best to either use a artist polyester fabric if you continue to use oil sticks or to switch to acrylic dispersion paints if you want to continue to use muslin. Unfortunately, due to the way in which acrylic dispersion paint dries, they are unlikely to be made into a stick form.  
To come back to my first point, we at MITRA hope that our users will take the current info about materials and processes into account to make your work as permanent as possible, but also understand that artists will sometimes deviate from best practices in pursuit of their vision. With this in mind, we also hope that we can offer alternate methods which may allow you to create the same effects but with more archival materials.

​I have sent a note to R & F about this thread and hope to hear a response about some of the issues mentioned here. I have other comments about your latest post but will wait until we have heard from perople with expertise in oil sticks.

​​I agree with the answers already given by Kristin, Matt, & Brian and have nothing new to add regarding oil paint on on unsized fabric. But I do have one suggestion, which is to try painting on a lightweight metal screen and let the paint go through that. You do mention needing to wet the support to extend drying time. But keep in mind that the various brands of oil stick have different consistencies and different drying rates, so you may want to research that.
Richard Frumess
R&F Handmade Paints

The silkscreen industry designs and uses a variety of Polyester materials according to the needed images to be screen printed or by the (Mesh) required for the printing. You might look into silkscreen polyester as a source as it is designed to last under extreme solvents; e.g. Xylene, Acetone, Mineral Spirits, etc. Just a thought
Martin Kotler 

1. Do you think one would be better than the other (pros/cons)? Honestly it sounds like you should go for working with silkscreen as you are after a bleed-through effect anyhow. I cannot see how one would be “better” than the other in terms of longevity, they are simply different but others may weigh in on this with additional info.

2. Would artist polyester also handle extreme solvents?
What do you mean by extreme? I cannot see why you would need something else other than mineral spirits. So yes you should be fine with that.

3. Would oil work vs. ink on silkscreen?
I do not see why not? As we have never tried this personally we would encourage you to experiment and please report back on your experience 🙂

4. Silksreen would be difficult to staple onto a stretcher correct? No. In fact this is how it is often prepared when used in the traditional sense.

One additional suggestion: If oil paint sticks are the final choice of medium, replace the poppy oil used for wetting with a low-viscosity alkyd medium. Poppy oil is known to yield a less flexible film than linseed, and I think flexibility and tensile strength of the dry film will be important here.

Also, I really like Martin’s suggestion to explore screen printing mesh.