Step 5: Painting
Now that you have it completely smooth its time to paint. Even though you have the surface super smooth the paint will still stick. If you are using Krylon Fusion paint because it is meant for plastic, which is even smoother than you have your surface now.
Paint as desired. I used 3 coats of flat black to minimize glare and show depth better.
If you are looking for a mirror finish you can read this instructable.