(I may of said this before, so ignore it if you have to)
It's a good excercise, drawing on envelopes. I timed my self, did about ten in 60 minutes. Banks in Canada leave a lot of envelopes by their main location ATMS.
I didn't finish them, instead had the group play with the envelopes and add their own flair.
It's a great when you have new memebers coming to their first meeting. It's a good icebreaker. Envelopes hold up well to light watercolor washes.
I was planning on leaving them at the ATMS to see if people use them, the bank keeps them, or people take them home to collect.