These alloys are chemically produced and processed by powder metallurgical techniques. The oxide content ranges from 8 to 12%. Tin oxide alone does not confer the required electrical characteristics and so it is used in combination with other oxides to tailor the properties to the application. The most popular grades are those using Bismuth Oxide to give good arc quenching characteristics and a consistent contact resistance throughout the life of the contact. They are generally supplied as silver-backed strips.