I am pretty new to painting outside and I have a Coulter easel. My question is - how do you clean out the wooden surface of the oil paint when finished so it is in good shape for the next session? Right now I am painting right on the wood and scrape the paint off and the wipe down with mineral spirits.
That is pretty much the way many do it. Over time that wood will develop a very nice grey patina. You could get a piece of tempered glass to put on top of the wood if you don't mind the extra weight. I carry along an extra palette that I hold just because I'm more comfortable painting that way. I've seen folks use the throw away paper palette pads and tape down a new sheet each time before they paint. I've done that too, and it works well... I do keep a plastic lidded container for keeping left over paint. I put all the extra into my little plastic container and pop it into the freezer when I get home. Just before I leave for my next outdoor adventure, I pull it out of the freezer and transfer them to my palette when I set up.
There's nothing wrong with the way you're cleaning it. The palette will turn gray over time, which is what you want and if you keep it up, the surface of the palette will become smooth as glass. But, you do need to make sure you keep up the regimen.
I simply cut down a pad of palette paper to fit the size of the box and tear off the sheet after its use when I need to begin a new one. It's lighter than a piece of glass and seems to save me time and mess.
Plexiglass...lighter than glass, easy cleanup.
Thanks so much for the variety of ideas for how to clean or "treat" the surface of my paint box!