Using Kitchen Appliances When Crafting?

I'm interested in making some crafts using things in my kitchen, such as melting crayons in a muffin pan to make new crayons, melting down old candles to make new, making clay ornaments with cookie cutters, etc. I've heard Playdoh and some other types of clay shouldn't be used with cookie cutters you plan to continue using, and you shouldn't use the same blender to make paper as you do to make smoothies.

I was wondering if it was the same with crayons and other types of wax, as well as homemade Playdoh and the like. I really have too many crayons from restaurants, broken crayons, etc. that I want to get condensed and the same with the old candles that were given to me. I don't however want to make my family sick because I didn't find out first. Thanks.

By Jessica