I purchased what we think is a brass possible screen print or such to hang as art on the wall. I started cleaning it but now not sure. Magnet does not stick but when I started cleaning with Brasso, it started revealing these strange squares underneath???? EEEEk! The thin sheet of supposed brass is over an MDF board so am baffled as to why these square outlines are showing through????

So I stopped Brasso and went to toothpaste cleaner....the dirty supposed brass reveals a silver color than back to brass---is this common with real brass or brass plated or is this an entirely different metal?

I've stopped working on it to see if anyone has any insight or tips. I regret cleaning it at all & should have just hung it up as is. Now I'm debating if I should keep cleaning and paint with Rustoleum "brass" color paint or not. If so will the squares still show?