For many centuries, silver has been regarded and valued as a precious metal. More abundant than gold and therefore not as costly, silver metal has often functioned as a coinable monetary system. Beyond currency, silver has numerous applications such as jewelry, ornamentation, tableware, water filtration and as an investment in the form of bullion, to name a few. Silver is used industrially in electrical contacts and semi-conductors as it possesses the highest electrical and thermal conductivity of any metal. Other applications include mirrors and window coatings, as well as in photographic film and X-rays. Dilute silver nitrate solutions and other silver compounds are used as disinfectants, added to bandages and wound-dressings, and incorporated into various medical instruments.