Sealed palettes are pretty affordable, about $5-8 depending. But if you are unlucky enough to have an unsealed palette, here is what you can do.
There are many ways to do this, including shellac, cheap oil from the hardware store, et cetera. My method is very simple. If you are an oil painter, you probably have a bit of linseed oil laying around. Take a brush, any smooth synthetic brush will do (don’t use your sable or camel hair brushes), dump about a half dollar sized circle in the middle of the wood, and spread the oil out with the brush. Let it sit over night.
If you have a very pricy unsealed fancy full wooden palette that you want to keep around for decades, I recommend adding about three layers of linseed oil once per year. But sand it down a bit between each layer to keep it smooth.
The purpose of sealing the palette is to reduce the absorption of oil from the paint itself, and as such, making it easier to clean. Plus, it looks pretty.
Clean the palette with a palette knife (do not use a razor!!!) and gently scrape the excess into a paper towel. Wipe out the rest of the paint with safflower or linseed oil and a paper towel.
Be careful with soaked rags and towels, they can spontaneously combust! Keep these in an fire safe metal can if you choose to clean items with oil and cloth.
The Quinacridones and Phthalocyanines colors are going to stain your wooden palette no matter what you do.
A safer and easier to clean method is to get a tempered glass palette, scrape off the excess with a palette or razor blade, and use Windex to clean the glass. Or easier still, use a disposable paper palette or wax paper, and just toss it into the garbage once finished. Phthalo blue and Quinacridone Violet will not be a problem using those two types of palettes. Basically, I ran out of paper palettes, and forgot to clean my glass palette months ago, couldn’t find a razor blade, and as such, this ‘how to seal a wooden palette’ came into existence… 🙄