Reusing the foam plates

Hi there,m going to post how i reuse the foam plates over and over again with my student.I have a large number of student who passes in the atelier ,so i have to figure out how i can be quick with the cleaning dilemma,so instead of spending lots of time to clean those plates,or the ones with colors that don't wash away quickly,i coverd all these plates with foil,and start to put a fresh paint on it,and after finishing i trhow away the foil,i can even start putting foil from the start before even staining the foam plate.thanx for reading.