About: http://webisa.webdatacommons.org/56068418

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	Although iron content may be one of the relevant factors, nevertheless organic, e.g. peaty colouring matter, would usually be the principal cause of discoloration (cf. specification, page 2, lines28-29).
http://www.w3.org/ns/prov#wasQuotedFrom	epo.org