Solarization

This is my favorite picture of my four I have done. I put it into the developer for about 20 seconds, took it out and after that I exposed it for 2 seconds. After that I did the regular process. The pictures I put less in the developer for the first time where lighter and there was more a difference between the black and the white. The longer it was in the developer, the more dark the white got's. It turned more to a grey-ish tone.
I would use this process if I want to show the differences between the black and the white. If I only want that the viewer sees the shape of the things in my pictures and not the detailed stuff.