Mystery of Picasso

This is a small piece of a film I watched, years ago, showing Picasso painting. This looks like an oil painting or maybe acrylic, since you can see him painting white over black, something you can't do in watercolor or ink.

In the film he starts out by painting ink onto the back of stretched paper on a frame that is lit from the front. All you can see are his brush strokes as the painting forms. It's very interesting and I recommend watching the entire film.

:::UPDATE:::
Apparently the video that I was using as an example of the movie has been taken down by You Tube, due to a copyright claim. Used in an editorial way it clearly falls under fair use but since I'm not a lawyer (and have no cash to hire one) we will have to put up with it.