Solarisation (or solarization) is a phenomenon in photography in which the image recorded on a negative or on a photographic print is wholly or partially reversed in tone. Dark areas appear light or light areas appear dark. The term is synonymous with the Sabattier effect when referring to negatives, but is technically incorrect when used to refer to prints.
In short, the mechanism is due to halogen ions released within the halide grain by exposure diffusing to the grain surface in amounts sufficient to destroy the latent image
In the darkroomCareful choice of the amount of light used and the precise moment in development to provide the additional exposure gives rise to different outcomes. However, solarisation is very difficult to manage to yield consistent results.
As a guide, an exposure of 1 second to a 25Watt lamp at 2 metres distant at around the end of the first minute of a 2 minute development can produce acceptable results. If the exposure is made with the developing print still in the tray of developer, it is important to stop agitation at least 10 seconds prior to exposure to allow any bubbles on the surface to disperse and to ensure that the print is lying flat. Solarising colour prints is more difficult because of the more careful control of temperature and timing that is required and because most amateur processing is undertaken in a processing drum rather than a dish.
In colour photography, different coloured lights can be used to effect solarisation, but the results become even less predictable.
It is possible to solarise a negative and subsequently solarise the print made from that negative. The results of such double solarisations are rarely successful, usually producing muddy and poorly defined images.
Solarisation in digital mediaGraphs describing solarisation curves typically place input range of tones on the x axis, with black at 0 and white to the right, and the output range of tones on the y axis with black at 0 and white up. A curve then defines the input to output mapping.
Early video synthesiser technologists concerned themselves with achieving arbitrary curves not limited by film chemistry. A goal was to extend the range of solarisation effects possible to a computer specified curve. They then applied the defined solarisation curve to real time video images. A video lookup table was often used to implement this. Using this enhanced solarisation technology, still photos could also be passed through a grey scale or colour lookup table with the advantage that the effect could be previewed and progressively improved, instead of a procedure based on darkroom exposure calculations applied on a one time basis to a volatile light sensitive film or print, as described above. This was an especial advantage for creating colour solarisations with 3 primary colours.
Two versions of the same digital photograph, the version on the right is digitally solarised using Corel PHOTO-PAINT 8.