Glass. Matt rough surface on the writing side. Painted on the backside. Could be with grid, dots and the like. The thickness and transparency of the glass makes

Glass. Matt rough surface on the writing side. Painted on the backside. Could be with grid, dots and the like. The thickness and transparency of the glass makes the chalk-writings cast a subtle shadow which gives a pleasant aura of expression. I’ve met many kinds of blackboard in my career, glass is the ultimate in my opinion.