A type II superconductor is composed of metallic compounds such as copper or lead. They reach a superconductive state at much higher temperatures when compared to type I superconductors. The cause of this dramatic increase in temperature is not fully understood. The highest Tc reached at stardard pressure, to date, is 135 °K or -138 °C by a compound (HgBa2Ca2Cu3O8) that falls into a group of superconductors known as cuprate perovskites. This group of superconductors generally has a ratio of 2 copper atoms to 3 oxygen atoms, and is considered to be a ceramic. Type II superconductors can also be penetrated by a magnetic field whereas a type I can not.