Abstract: A method for forming a hermetically sealed capacitor including: forming an anode; forming a dielectric on the anode; forming a conductive layer on the dielectric thereby forming a capacitive element; inserting the capacitive element into a casing; electrically connecting the anode to an exterior anode connection; electrically connecting the cathode to an exterior cathode connection; filling the casing with an atmosphere comprising a composition, based on 1 kg of atmosphere, of at least 175 g to no more than 245 g of oxygen, at least 7 g to no more than 11 g of water, at least 734 grams to no more than 818 grams of nitrogen and no more than 10 grams of a minor component; and hermetically sealing the casing with the atmosphere with the capacitive element contained in the casing.