About: http://webisa.webdatacommons.org/403737561

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	However, since PbO is a harmful substance, the incorporation of PbO into an optical glass is being suppressed in recent years.
http://www.w3.org/ns/prov#wasQuotedFrom	google.com.au