As Fast As
You Can
While in school, I participated in local art shows and sold paintings, drawings, and prints as a vendor. One of the ways I attracted clients was by performing 6 minute drawings of whoever or whatever they wanted me to draw.
Clients usually came to me with a picture of who or what they wanted a portrait of, and some even insisted that they hold still for the entirety of the 6 minutes until their portrait was done.
Each piece was timed and done using the flat side of a compressed charcoal stick, and if clients were unsatisfied, they were under no obligation to compensate me, or I would draw them another until they were content.