Storm in a teacup

We always use the same brand of teabags. Even 10 years in NZ did not stop me from using Yorkshire Tea. Friends and family would bring me some every time they came and send as gifts before realising I could source them out there :-) Nothing has changed but every so often we get this film on the cups not sure why or how but it fascinates me the way it kind of breaks up as you drain the cup.
Weird blip I know but there you go!