I have had a small stack of natural colored picture frames in my "to do projects" stack for some time now & I finally got to them! I'm very happy with the out come.
I sanded them all down with a 220 grit to not score the wood but get any varnish off so that my paint would adhere to the wood. The higher the number on the sand paper the softer the grit.
I then painted them black to go with my 2 hanging large picture frames. To seal them & give them a slight shine, finish them off with "Mod Podge" (matte finish). It's milky when you put it on but dries clear.