Digital BW, The Print

Come to find out Georges Seurat did do some BO painting early on but
eventually gave it up. Evidently for two main reasons: 1. When he
learned that all black pigment was really made up of all his colors
mixed together it began to loose its aura for him. 2. Degas ribbed him
so much about the coarseness of his high values that he just stopped
and embraced the entire spectrum of possibilities.

Its all here in the video: 

http://www.roland-collection.com/rolandcollection/section/12/415.htm