I don't recall there being a requisite # of ranks. But, off-hand, I would say 6 ranks would be reasonable before some one believes it's worth their time to pass along their knowledge & possibly secrets. Libram Novus #5 has a table of Ranks/Title. I'd use that and scale it up 1 level. So, in order to be accepted as a Novice by an Alchemist making swords, you'd need to be at least a Journeyman Sword-Smith for example.