Stamp of Approval

I just bought the new Total Solar Eclipse commemorative postage stamp. It turns out to be heat sensitive and will change image!  Very clever and fun.  (When's the last time you said that about a stamp...?)

By default, it shows a total solar eclipse, but if you press a finger on it the eclipse goes away to reveal the earth.  But it's the gift that keeps giving, since when the stamps cools it will revert to the default eclipse.

By the way, any heat will work, not just pressing a finger.  The post office official told me about someone saying that they left a sheet of the stamps in a car, and when they got back to the overheated vehicle the stamps had changed.