The 5% tin content of my soft jig head lead significantly retards surface oxidation altho I do store the ingots in closed cardboard boxes in a shed for future use. The hard wheel weight stuff seems to stay shiny in the boxes as is.
MLAL, since you enjoy the melting and casting, you should allow a FLOW of lead into and out of your life. You know, convert scrap into saleable castings. The money you make can be allocated to further supply aquisition and you will be bizzy doing what you love. Lead sitting in storage is dead lead of no value to anyone, unless you consider it a commodity investment.