Using the Sun
I've started to look at three photographers using a similar concept. Chris McCaw, Hans-Christian Schink, and Jonathan Kline. It seems that Chris McCaw may have tried out the idea first, but it's hard to know for sure. Some photographers put a lot of photos on their websites, but omit the year it was created! All three make very interesting photos. Timed exposures using the sun to either burn marks in a paper negative, or the use of a pinhole camera with film - even though the idea is basically the same, they each have made it their own.
Candela Books has published a book of Chris McCaw's work on the Sunburn images.