WHY IS MY CHALKBOARD MAGNETIC?

little did i know, but most modern chalkboards are made of steel:

The highest grade chalkboards are made of a rougher version porcelain enameled steel (black, green, blue or sometimes other colours). Porcelain is very hard wearing and chalkboards made of porcelain usually last 10-20 years in intensive use.

and what about chalkboards evil nemesis, the whiteboard:

The white background can cause contrast problems for people with vision impairment.

i guess thats settled.

additional info here.