I am all for a canning recipe thread.
Basically it makes the aluminum which what the OP and me have for a pressure canner become malleable enough that the inside pressure makes it look like a round pot instead of a cylindrical pot like it comes.
It ends up screwing up the seal, the flat bottom(which becomes round), and all your stuff you are canning inside.
Now you have to buy a new $80 Canner :-( I wish I had pictures before I took it to the scrapyard (which gives you less per pound aluminum scrap than used cans) but I was too depressed at the time.