1. Clean the glass and remove the frame.
2. Use chalk spray paint directly on the glass and flat white (or anything) on the frame. (Rustoleum is my favorite!)
3. After a few coats - voila!
4. Make sure to allow the chalkboard paint a good 24 hours to dry. I didn't and some of it scraped up while I wrote and I had to re-do it.
5. Once it's dry, take the chalk sideways (no sharp edges) and rub it gently all over the board. Gently rub it off with a rag. And now it's good to go.