keep centered

I'm about to set off for a 2-day workshop on making brushes taught by this gentleman: http://www.grishkoffstudios.com/workshops/AdultMain.html
I like Glenn and his work a lot, but I am also wishing for history and documentation on the brush beginnings, which logic tells us are quite old. But most non-SCA workshops just touch on the history of what they are teaching and focus on the aesthetics, which is also good. I've been doing just a little research online and haven't found anything.
At any rate, it will be good to take the workshop and make some very cool brushes.