This is a mezootint print, which is a drypoint technique. It means that you first completely scratch the plate witha rocking iron. When printed like this, it gives a completely black result. Afterwards you can polish certain areas to create grey and white areas.
A hippo is my favourite animal, but it still took me several years as a graphic artist to make a work around it. I feel the mezzotint is a great technique for this majestic animal because it gives a mysterious and dangerous aura.