Neil Leifer left his Boston law firm two years ago after spending 20 years litigating cases involving children’s lead poisoning. He sued lead and lead paint companies and property owners and managers on behalf of children with lead poisoning. In 2008, Leifer cofounded a nonprofit that helps ceramic artisans from rural Mexico convert from lead-based to lead-free glazes. The Globe spoke with him in advance of the Dec. 15 pottery sale to be held at Thayer Academy in Braintree.