Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

If my citric acid and steel wool didn’t do it then it’s not mineral deposits. I thought the glass might have been etched but it still feels smooth. I think that whatever it was might have actually chemically changed the glass. I put the new one in so I’m not really worried about it. I’m just very curious as to what could have happened. I figured that I’m probably not the first one to see this, and wondering if someone could satisfy my curiosity.