I also cleaned my ground glass with soap and water and removed all the grid lines. Fortunately the grid lines are faintly etched into the glass I have so if I want to I can draw them back in (I suppose). I've never felt that I needed to though, as I can see the etched lines if I look for them. The ground glass on my 4x5 had a lot of tar and discolouration from being in a room with heavy smoke for a number of years. It works fine now.