<http://schema.org/about>
"Go to any dump or propane refill station and you will see hundreds of empty tanks; after 10 years they cannot legally be refilled without testing and recertifying, which is more expensive than a new tank. Artist Shirra Wall puts them to use, cutting"^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.treehugger.com/sustainable-product-design/art-from-old-propane-tanks.html>