I have some double walled glass coffee cups that I use every day - I make cappuccino in them, so there is often a thin film of milk foam left.
They then sit in the dishwasher for three or four days until I have enough of a load to wash (I live alone so it takes a while).
I haven't been rinsing them first, partly because I use the same glass for a second or third cup over breakfast.
They've always looked clean when they come out of the dishwasher, but I've noticed now if i hold them up to the light, there is a very thin film still, with spoon scrape marks! It's very thin; washing it with a scrubby sponge doesn't do much to it, so it's pretty firmly on there. I've tried the glasses cycle in the dishwasher, and tried vinegar, but I'm not sure what else I can do to get it off. I'm not worried that they aren't clean, as nothing comes off to the touch, but it looks a bit grim and I'd rather they were sparkling!
What else can I try?
I know i'll probably have to start rinsing them every time before the dishwasher, but I need to get them clear first.