Handbags   (The sad, the bad and the ugly. Non-productive stuff here.)

How come tea stains (tannins, I think)deposit on the inside surfaces of my cups (ie mugs), but NOT on the inside of my tea pot?

They are from the same set. Made of same materials, as far as I can tell: same decoration, same glaze.

Also, I do not take milk or sugar, so the contents of both are identical.

Only difference I can ascertain is inside of tea pot is not exposed to light, so perhaps photochemistry at the base of this.