Tip 1: Often, I have oil paint left on my palette after a painting session. More importantly, I have colors I have blended for the painting I am working on. I have tried many way of preserving these. I have used glass palette and simply submerged them in a tray of water. This works overnight quite well.
Another way I have come up with to preserve a palette is to use wax paper over my wood palette, or waxy disposable palettes. I simply cover them with either another piece of waxed paper or another disposable palette, and freeze them. This will keep the palette longer. I have never had any trouble with the paint after it has thawed out. It doesn't seem to effect the paintings either, as I have done this for many, many year, and have never had any trouble with any of the paintings.
Tip from: Susan Tschantz.
Tip 2: After a lifetime of fighting the lumps which accumulate and ruin expensive oil paint, I happened on a solution. I was watching a video and the artist (Johnnie something?) recommended using a glass palette and storing the oil paint underwater. Sounds crazy, but I have been doing it for several years and it works great.
I have kept the palette and oils submerged for weeks and had no loss in workability or performance. (Unlike storage containers or plastic wrap) The paint is completely unaffected by the water, though after some time, the blues and greens get a little hairy fungus starting on them. It's then probably time to change the water or start with fresh paint.
Tip from: James Knauf
[Note from Painting Guide: For a scientific opinion on whether storing oil paints under water is a good idea, see FAQ: Freezing Oil Paints.]
Tip 3: I bought 20 empty 35mm film cartridges [containers] from eBay for a pound. At the end of a painting session with a palette knife, I put my paints into the cartridges. As they're airtight the paint keeps for a long time. I've also labeled them.
Tip from: Ken Robson
Tip 4: I took some lessons from a lady who used Styrofoam plates Tip from: Vanbella
Tip 5: With oil paint so expensive these days, no one can afford to scrape off their palette and just throw away the paint. I use a seven-day plastic pill holder to store any leftover paint. When I am done painting for the day, I mix together all the colors on my palette which usually turns out a wonderful gray. Then I put it in one of the day slots, close the lid and put it in the freezer.
Often I take it out and use it the next day to continue on the painting where I got the scrapings from. The gray works well as a medium ground for the painting because it is made of the same colors in the painting. Or, I collect the grays over a period of time and when I need just the right gray, I take it out and it is like new. It is also fun to do a painting with all the grays I have collected.
Tip from: Judith D'Agostino