I used some petrified coral I got from a family member, which they got from a coast vacation from before I was born and used it. I just boiled it for a few minutes to be sure. I have also purchased some from a garage sale and just hosed it off real good and still didn't have any ill effect. If you know the history you can probably skip the boiling. I only boiled the ones from the family member because there was moth balls in the box. You know how the old folks like to store stuff with moth balls.