I have a mug that when you add hot liquid, it reveals some secret message.
Just thinking out loud .... Adding hot water, then Eve uncovers. Maybe not for your man's work ... but it could be very cool !!!
Here's an example. But if you can get your hands on the thermal coating ... you could have some fun.
That is an excellent idea! Not sure I can do that but I’ll store the idea somewhere for possible later use :)
Sounds like a perfect valentines day mug. ;-)