As far as I read magnets loose their magnetic effect after heating.
Therefore you should remove the magnet before baking your clay project.
I used this snow for my snow ball.
To avoid the snow flakes from sticking together, mix the destilled water with a drop of dishwashing liquid.
... base for the halo
This is the product I used for this project ...
"Wasserklar für Schneekugeln"
It worked very well!