I used acrylic paint. The reason I like acrylics is because you can use them like oil paints and also like watercolor washes. In order for it to be completely smooth, with no paint brush lines I painted it in many layers. It was a relatively slow process because I had to make sure each layer was quite dry before I added another layer and I had to make it a really solid black and white. At the same time I had to apply the paint carefully to make the edges where black and white meet as sharp and clean as possible. I couldnt make any mistakes because the painting would be ruined. I was very satisfied with it and my customer was over the Moon with it.
I had never painted anything like that before so I surprised myself. After they came out so well I painted the one of Obama. Its a lot of meticulous work with all those edges and it takes patience, which goes pretty contrary to how I usually paint. It can get tedious because you cant just get lost in the zone.