On coffee mugs and such where heat makes a word or picture appear, (or disappear) how does that work? (more..)

Question

My son asked about that this morning. We have a coffee mug that when you pour hot liquid in it, makes a tiger appear on the outside. When the mug cools, the tiger disappears. He (and the rest of us) want to know how this "technology" works and what materials are used to make it work!

Answer 1

Its called Thermochromic paint.
The mug is probably using one called Leuco dye, the dye is suspended in microcapsules in a carrier.
When at normal temperature the capsule contents are solid and the dye is transparent.
when heated the capsule contents become fluid and salt inside the solution separates, this changes the chemical structure in the microcapsule and its ability to absorb light changes, you see this as a colour change.
Leve it to go cold again and the capsule contents solidify back into the Leuco dye and its clear again.

Answer 2

It's called a thermochromic ink

There's some info on Wikipedia under thermochromism

Try searching on either of those words and you'll probably find what you need