One of our ideas is to use hydrochromic ink. This is aan ink that changes colour when it's wet.
While we were still thinking about it, Kathleen said that it would be perfect if we had a material that changed of colour chen it was wet. So Hydrochromic ink would be a nice solution.
To buy hydrochromic ink we have 2 options:
But this company wasn't sure about the food safety of this ink and they said taht the ink wouldn't work if it's in water for a long time. The ink can also only be put on textile.