This year we're doing "Guys and Dolls" for out spring production. Our main set is the Mission (inside). My question is, what are some ways of making the walls and windows look old. The windows our an Ash white color with mission painted backwards on it, as if looking out of outside, and walls are like a Mustardy yellow color (not my choice). Right now they are painted so that in some spots it looks as if the plaster is falling off and you can see the bricks showing through. What are some other tips. Thanks. It needs to look really dingy and dirty. -Ray.