The title says it all...they are just regular ceramic glazed cups and, over the years, have become stained by black tea. Any ideas? No matter how "clean" it is, I am bothered by drinking out of a stained cup...
Apparently doing it rong and ruining it for everyone, but I don't give a crap anymore.
Baking soda! DH is a huge tea drinker so we get this a lot. Basically I just sprinkle some baking soda on a wet dishcloth, scrub the cup, and rinse. Sometimes the inside corners need a bit more work which you can see once you rinse - just put a bit more bs on it and scrub it again. Once it's clean I wash it with regular dish soap and water, otherwise the baking soda can dry to a white residue (not really visible on most cups though).
This works great on corning ware and baked-on food pans too. I keep a box under my sink for easy access.
I use those powdered scrubs like Barkeeper's Friend or the one I have now Bon Ami calls it a powder cleanser. it contains limestone, feldspar,biodegradable cleaning agents from corn coconut and palm, soda ash and baking soda. It works great for cleaning everything- tea stains, pyrex pans that have that cooked oil/food making them not clear- scrub with this stuff and they're clear again.
I've also had good results with straight baking soda- rinse cup and dump water out add enough baking soda to make a really thick paste and scrub that around.
I only found tea stains once I stopped washing my mugs by hand. So a 3rd vote for baking soda or even just a dish cloth. You just need a little friction.
If you don't want to scrub, the easy-peasy method is a splash of bleach in the cup (about a teaspoon) and then fill to the rim with hot water and let it sit for a half-hour or so. There are concerns about chlorine bleach though, so the baking soda method is probably best. Baking soda and vinegar combined may decrease the scrubbing you have to do.