[Mariana (OP)]

Ranjay wants to know:

What material can change colour when heated and reverse back when cooled in things such as cups and mugs, or children's plastic spoons?

Can you help?

[syhprum]

At school we were told we could judge the temperature of steel by the colours of the oxide film that forms on it, I think we have better techniques today

[Bored chemist]

At school we were told we could judge the temperature of steel by the colours of the oxide film that forms on it, I think we have better techniques today

The OP asked for changes that are reversible.
There's a useful start here
https://en.wikipedia.org/wiki/Thermochromism

[evan_au]

I have a mug at home with a black-and-white image of a Mondrian painting.

When you put tea or coffee in it, it changes to the real colors of the Mondrian painting (red, blue and yellow).
I assume that this uses thermochromic liquid crystals; unfortunately, it won't survive a dishwasher!

This was produced for the Museum of Modern Art in New York (but I bought it from an art gallery closer to my home).

[steverogger007]

This is really a great post

[Colin2B]

This is really a great post

But not such a great attempt to spam us.
Bye