In photographic terms Solarization is the process by which a photo is manipulated in the dark room creating a reversal of colors. Normally done in black and white photography to take advantage of the silver content of B&W photographic paper. This is done as follows: slightly under expose the paper with the negative in the holder, develop the paper but do not put it into the stop bath, squeege the paper off and place it back under the enlarger. Remove the negative. Stop down all the way (f22) to the smallest opening in the enlarger's lense and re-expose the paper. Develop as normal from then on. This process will cause white lines to be black and black lines to be white. The process works best with VERY contrasty negatives. It is possible to solarize color paper despite the lack of silver. Results very and it is once again best to have a very contrasty negative to work with.