I have always loved this image of the knees, in fact one of my darkrooms had this image in reproduction on the wall for inspiration.
I do a lot of solarization's, and if it is one it is a negative solarization, using a metol only developer.
The black maki line only is produced this way , a white maki line is produced with a print solarization.
If you want both then one needs to flash the neg and flash the print.
I really doubt this is one , as I would think we would see much more of this kind of work from him, I believe as most here it is a specific lighting condition, that is really , really cool.