Dutch Oven question

I'm reading a book on Dutch Oven cooking. The author suggests that when you're baking in a pan (like cookies, pies, or casseroles), to raise the pan off the bottom of the DO a bit. He suggests "unplated" washers so they will "not shed a coating or melt." I have lots of nuts from Tractor supply in grade 3,5 and 8. Each of them has a different color. How do I know if any of these have a toxic coating? If I throw them in my BBQ at the end of a few sessions of cooking will that take care of any complications?