I have a blot of oil paint about the size of a nickel that penetrated my Liquitex Matte Medium prime/size layers into the back side of the canvas (36×36 inches). It came from an early layer that was lean and thin, dilluted with odorless mineral spirits. This painting has been entirely dried and hardened for about 5 months. Given that the oxidation process of oil paint is no friend to cotton duck canvas (18-24 oz mine) what would you do to help the long term integrity of the painting?
I had considered applying acrylic gesso to the oil blot, or even the entire backside of the canvas, applying layers thinned slightly with water to soak deep and contain any oil leakage. I have researched (to no avail) the conservation of Francis Bacon oil paintings on raw, unprimed and unsized canvas which I sought as a precedent.
Thank you for your help!
It is true that linseed oil is acidic and can be deleterious to cellulosic fabric. It is best to try to avoid letting the fabric absorb drying oils but the situation you describe is not as dire as you are suggesting. One of the reasons that I write that is that there are historical paintings that were full impregnated with oil and oleoresinous materials to create a transparent support. De Mayern talks about this and it is mentioned in other treaties of the 17th and 18th centuries. Examination, analysis, and the conservation of a group of these paintings is covered in the paper, Not Preparation but Impregnation: Transparent Paintings. It is in the following book:
https://www.amazon.com/Preparation-Paintings-Artists-Choice-Consequences/dp/1904982328
This group of paintings has survived from the late 18th century. Although they do suffer from conservation concerns, most of these are not specifically about the rotting of the cellulose from the drying oil. They have darkened , become embrittled, etc. Now, the drying oil has a role in this so I am in no way advocating for saturation fabric with drying oil, I just mention it to allay fears of immediate destruction of your painting.
The remedies you are suggesting are likely to cause more problems to the support that the small amount of linseed oil absorbed into the support. If you add small areas of acrylic dispersion ground to the reverse, you will be creating regions that will respond differently to changes in the environment and the will likely telegraph topographically to the surface over time. Unless to you take the painting off of its stretcher, there is no way to evenly and completely cover the back. This would cause the same issue mentioned above. Additionally, the application of watery materials to the reverse are likely to cause distortions to the canvas, which may become locked in permanently when it dries. Finally, there is really no point in encapsulating the region of the fabric that has soaked up a little drying oil. If there is future chemical effect to the fabric, it would occur in the cellulose under these coatings anyway.
I suggest that you leave the painting as it is, it will likely be fine. Also, learn from this and make sure that you fully size the canvas before applying drying oil paint layers, especially those well thinned with solvent, to the canvas.
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