When I discuss sketching people on location during my Crealde Urban Sketching Class, I pose for the students and then ask each student in turn to pose for 5 minutes. 5 minutes is about the most time you might ever be able to sketch someone on location before they walk off or turn their back to you.
The key to sketching people on location is being able to guess how long they will be focused and sty still. Any time I enter a restaurant I look around to see how much food is still on the plates of the people around me. If their cups are full and they are deep in conversation then it is a prime time to try and catch a sketch.
All of my students in this class are amazing and they all sketch very differently from each other. It is possible to tell at a glance which student created which sketch. That is what makes Urban Sketching so interesting.
Everyone is now on board with trying to complete each sketch with watercolor and finalized ink line. Though I often sketch the line work first, it is sometimes nice to just throw down some large puddles of watercolor to define a person’s general share and then refine it later with line work. I did this sketch in the time it took for 4 students to pose. Rather than sketch the model each time, I sketched the model once, and then sketched the students at work around her. I break the cycle of only focusing on what is expected.