On my desk at school, I have a coffee mug and a water cup. I don’t wash either one of them. The coffee mug is blue, so the “seasoning” doesn’t show up as much as it might on a lighter color. The water cup is black. You would think that water wouldn’t leave any kind of residue behind, but it has. There are hard water deposits on my cup. So interesting…

It’s, er, bone-building?
Lloyd used to work with a guy that never washed his coffee cup. It was like an archeological dig site.
Nice coat, by the way!
This looks like the inside of Thurman’s morning coffee mug at home. He’s had it for decades and it only gets washed with soap and water once in a blue moon. In fact, it IS a (dark) blue, so like your water cup the “residue” is fairly hard to see…but believe me, it’s there. He hasn’t died yet, so there’s hope for you as well, friend. 🙂