You want to be careful not to get into a power struggle. I think by giving
them the consequence of their behavior (they will spend x-number of classes
without access to the disrespected materials & they will write art
definitions) sounds O.K. however, I think I would leave off the
expectation/requirement that the guilty party come forward. Although it may
seem unfair, if the whole class receives the consequence the peer pressure
may take care of any future problems. I would give them lined paper &
pencils to write their definitions. If you require them to bring them, some
will undoubtedly challenge you & show up with nothing. Then what? You'll be
in a power struggle thing & that's a road you don't want to go down.
Good Luck! We'll be anxious to hear how this works out for you.