At work we had a 4'x4' powder coated sheet of aluminum hung up in one of the engineering offices as a white board. It worked fine for about a year. We moved out

At work we had a 4'x4' powder coated sheet of aluminum hung up in one of the engineering offices as a white board. It worked fine for about a year. We moved out of the office for some construction and when we moved back in we took some markers from another marker board. I drew a diagram to illustrate an idea, and when I tried to erase it it wouldn't come off. We tried a few more markers, and it seems that for the same family of Expo markers some colors erased from the powder coat and some didn't. The usual solutions (denatured alcohol, overwriting with an erasable marker) didn't work. Only acetone would take off the green, yellow, and purple marker. And the acetone seemed to literally peel off a layer of the powder coating under the marker, marring the surface and ruining it for further writing. I guess you live and learn. We got a proper whiteboard to replace the metal panel.