The tip about freezing of oil paints to preserve them between painting sessions, usually suggested as placing your entire palette in the freezer, in based on the fact that oil freezes are a very low temperature. (It's far lower than water.) Given the temperature a domestic freezer is usually set at, leftover oil paint put into it is unlikely to freeze because it doesn't get cold enough.
I put the question to about freezing oil paint to Anne Marie Helmenstine PhD, About.com's Guide toChemistry, who said: "The freezing point of linseed oil (the predominant oil in oil paints) is -20°C (-4°F). Most people set their freezers at 0°F, so oil paint will not freeze in most home freezers.
"Oil paints work better when applied at cold or even freezing temperatures, but the paintings themselves are embrittled at low temperatures, especially if the humidity is low. It's fine to store your oils in the freezer if you're taking a break. The cold temperature will slow the rate of oxidation and evaporation, preserving the paint. But once you start a canvas, it's better for the painting to maintain it at a room temperature that's cool but non-freezing, otherwise the painting may become brittle."
An article in issue no 12 of Golden's Just Paint by a "scientist who specializes in coatings" says this about freezing oil paints: "Oils also become more brittle when cold, but embrittlement occurs at temperatures below freezing. ...significant drops in temperature from 23°C down to below freezing at very low humidity can create stresses in a fairly young 13 year old oil paint film that will exceed its breaking point."1
