Thanks all.
I picked up a Sweetgum bowl blank over a year ago on a lark, and was amazed by how beautiful it is. Now I plan to get more every year.
Tony - Aside from what you describe, I minimize opening of the can. I try to wait until I have a few things to finish and do them in a batch. I pour a bit in a cup and do one coat in the morning and one before bed. That way I only open the can once a day. My current can is 9 months old and starting to thicken a bit. I also keep the can in my basement where it stays cool.