Oxidation happens in the presence of--ta da--oxygen! Humidity has naught to do with it, in my understanding. I put new-cast balls in repurposed glass jars with good gaskets in the lids. Screw 'em down snug. The oxidation will take place until the oxygen is taken up by the process. Viola! No more oxygen in the jar, oxidation stops. I have balls I cast maybe 20 years ago, and they remain in the unopened jars, nice and bright. But if you are in the habit of often opening the jars to remove a few balls, you are putting fresh oxygen into the system, and the process begins anew. It works for long term storage, which is why I use smaller jars, holding maybe 8oz by volume.