Do you know sun printing?
For this fun technique you need special nature print paper
which is also called solar photo or sunprint paper.
You arrange your items on the paper
and expose it to the sun for a couple of minutes.
It will then look like this:
The exposed spots have turned very pale
and where your items lay the blue remains.
Then follows a short water bath
that will "develop" your prints
and reverse the colours:
Magic, isn't it?