it 's a very brief post on etching with some photos but not to much detail .
Yes he dos uses a old crockpot and air bubbles but no temperature setting were on the post .

Rob (spikkkkkkk ) over on rcgroups.com
[link]http://www.rcgroups.com/forums/showthread.php?t=1319543[/link]
gives some info on etching Alum but again not a lot of detail