Masterpiece?

[davidjackson]

Secret society is, perhaps, a misnomer here. The term in the late middle ages is used to denote the master guilds. Such guilds, especially the German ones, would often insist that to become a master craft man you had to produce an exceptional piece of work, and often they produced private how to books to help and train initiates. But the usual ideas we attach to such a thing - guttering candles, hooded robes in shadow, you get the idea - probably didn't exist! 
This tradition is visible in the 16th century kunstbuchlein, a series of popular printed works that drew on earlier private manuscripts from the guilds and was the first self help range of books.