Originally Posted by Grotius
Also, a somewhat off-topic question: do people ever use paper mattes with oil paintings? My sense is generally no. Why is that? Is there concern that paper overlapping the canvas might not let the oil breathe, or some such?
The reason I don't use cardboard mats with framed oils is because there is no protection for the cardboard since I don't use glass when framing oils. The mat will remain exposed to dust, moisture, finger prints and airborne pollutants. It will eventually become pretty ugly with no way to clean it. The oil painting itself, particularly when it has a removable conservation varnish is well protected from such things and can be easily cleaned as needed.
One of my best paintings that started out as a quick study, was done on some Canson canvas textured paper. I left a plain white border around it from the tape holding it to my easel panel, with no intention of leaving that showing later. It looked really nice with this particular painting, so I ended up painting some white oil paint over the white border, mounting it to some ACM panel when dry, then sealing it with a permanent layer of Galkyd Lite so I would have a durable surface over the entire piece including the plain border. I then finished it off with some Gamvar. I felt it was at least as durable as a stretched canvas so I ended up framing it like I would a piece that was done on canvas or prepped panel.
Fabric liners are generally what are used in place of mat board liners / mats with oils since they are more durable. They do tend to collect contamination, just not as readily as paper products. If the fabric used has been sealed / painted like an oil painting, they can be cleaned later as needed without damage. I have seen mats and liners made from wood, hardboard and even metal that were painted or sealed somehow so as to make them more durable. Some have been very attractive, adding to the overall presentation, some have been pretty nasty looking.