In 1896, Tesla was issued a patent for a corona discharge ozone generator using charged metal plates to act on ambient air. He formed the Tesla Ozone Company and went into production of these units. His customers were naturopaths and allopaths who welcomed this powerful therapy into their practices. Breathing of ozone bubbled through olive oil and other oils was widely practiced at this time, and the Sears catalog of 1904 offered a unit for this purpose using eucalyptus, pine and spearmint oils. Tesla produced a gel made by bubbling ozone through olive oil until it solidified, and sold it to doctors.