I had this activity on our to-try list last year, but Massachusetts never got very hot. This summer has been plenty hot, so I thought we’d give it a try. We cut the tops off of some plastic cups, added pieces of crayons, put everything in some left over aluminum foil. We covered it with plastic wrap at the suggestion of my mechanical engineer brother, who happened to be visiting when I decided to try this.
I didn’t try it on the hottest day – temperatures were low nineties, and some of the crayons didn’t melt. I think they were from the cups that wound up partially in the shade, and I think they were also washable and twist-up crayon pieces, which may have affected our results.
We’ll probably try again on a hotter day, but these crayons work well, even in their imperfectly-melted state =)