Solarization (also called the Sabattier effect) is a traditional wet darkroom technique most famously known in the work of Man Ray.
The effect is produced in the darkroom by a short, intense exposure to bright light during the development stage. In the early days of photography a flame would be ignited in the darkroom, flaring brightly for a moment and then extinguished. I used a small portable electronic flash about 17 seconds into the 25-30 second development stage.
Note the distinct shadow reversal in this image of the (deformed) talons of a Bald Eagle.
The most noticeable result of solarization in Life: As We’ve Known It is the reversal of shadow, producing a light tone where a dark shadow would normally be. While a shadow typically contextualizes and anchors a subject in its environment this reversal of tone serves to visually "lift" or float the subject from the background.
Another is the Mackie line (example below). This thin, dark line forms along a boundary between light and dark areas, typically between areas of high contrast. The Mackie line only appears on the Polaroid film negative, not the positive Polaroid print. You can clearly see this line in many of the final artist prints.
On the left a dark Mackie line appears clearly along the breast of the crow and the shadow on the right is lightened - both specific results unique to the solarization technique.