Demarcate the Paint Zone
If you wish to use only a specific area of the glass as a chalkboard, you will need to demarcate the zone using artist's tape. These tapes never leave a sticky residue, so do not worry about dust settling on the border! Now, spray paint within the demarcated zone, and once your done adding the extra layers, wait for the paint to dry, after which you must gently remove the tapes.