Black paint.
Linseed oil and lamp black is how black, oil based paint is/was made. I'd use an oil based black satin paint if I were to paint it.
I'd probably stain it, however, with oil base, semi-solid Cabot stain+sealer. The stuff lasts forever with proper preparation and proper application.
Or you can mix up a batch of your own paint. Lamp black and linseed oil can be purchased easily.
