1. Solarization
An Alternate Process
By Gerard Vanloo

2. Some History
Originally described in print by H. de la Blanchere and again by L.M. Rutherford
Named the Sabitier effect, although, he did not describe this effect first
Accomplished by first dropping the picture in developer and the stop bath, and then exposing it to light once again. Then go through the same steps as normally.
Make sure there is no film in the enlarger!!!
All about timing in terms of both original and final exposure.

3. Sources