I've encountered lots of chalkboards through my career, and they vary widely in quality. Some write smoothly and erase cleanly; for others, the chalk squeaks and the eraser just smears.
I assume there are differences in the materials they use, the construction techniques, how the surface is prepared or treated, and so on. But I'm clueless as to what these differences might be, and how they affect the quality. If I'm looking for a "good" one, what questions should I ask?
(Academics are one of the few groups these days that use chalkboards on a regular basis, so I hope this question is suitable for this site. Please note that I'm not asking for specific product recommendations, just general information.)