Marco, this is a very inspiring series. I'm partial to this one in particular. Nice work.
Are the darker edges a product of the pinhole camera or brush development?
The dark edges are caused by the light fall-of in the pinhole camera. The Zero Image 4x5 camera is a super wide angle pinhole (about 130 degrees view, the camera is just 2-3cm thick!) and uses the normal flat film cassettes, as for a 4x5 viewcamera. So there is unavoidably a lot of light fall-of to the edges.