Period 6 element form, as an X-ray radiocontrast agent for imaging the human gastrointestinal tract. Soluble barium compounds are poisonous due to release of the soluble barium ion, and have been used as rodenticides. New uses for barium continue to be sought. It is a component of some "high temperature" YBCOsuperconductors, and electroceramics. The lanthanide or lanthanoid (IUPAC nomenclature) series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium. These fifteen elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements. The informal chemical symbol Ln is
Tibetan silver iron 'cheese metal' casting, overlaid with this pewter and silver plating. Dependent on source, these can be either thick and robust, or attractive but easily broken due to a loose, fragile inner casting. The latter productions are therefore only suitable for small castings up to around 12 mm, or transient 'fashion' jewelry with a short lifespan. Tibetan silver Tibetan silver is used primarily in jewelry components, and is similar to pewter – an alloy of copper, and sometimes tin or nickel, with a small percentage of pure silver. Its overall appearance is of aged silver, but it can be polished