"I drew most of the sketches on location. It usually takes me 10 mins to 1 hour to finish one, and I'm still trying to improve my speed. My father always said sketching has to be fast! If it takes too long, then it won't be a sketch but a drawing or painting instead. When you do it fast, you can capture the essential element/subject and not spend too much time working on the details. And for humans, for example, they will never stay still longer than a few minutes."