I was excited to see your advice since I have been having this very problem with my clay lidded jars. I would like to try Alumina however an online search reveals all sorts of varieties:
Research Grade a Alumina Powder 10-15nm, Research Grade a-Alumina Oxide Nanopowders 150-500 Nano, Alumina 30c (Health and Beauty)
Can you advise which type I should get?