I bought these silicone heart shaped trays from the Target dollar bins a few years ago. I'm pretty sure I've seen them at our Dollar Store too. These were perfect for making heart shaped recycled crayons for Valentine's Day.
The first thing you need to do is set your oven to preheat to 200 degrees. While the oven is preheating, choose the colors you want to use for your crayons. The better quality of the crayon, the better it will melt and hold together. Peel the paper from your crayons and break them into small pieces.
Place the broken crayons, into the tray. You can group like colors together or mix them.
Place the silicone trays onto a cookie sheet and bake for about 15-20 minutes, keeping a careful eye on the melting process. When the crayons look fully melted, remove them from the oven and allow to cool for about 10 minutes, then pop them out of the mold.
I used glue dots to attach them to small cardstock cards as Valentine's for my daughter's preschool class. We also put some in a goodie bag, tied off with ribbon, to give to the teacher for the class to use.