Solarization

Pseudo-solarisation (or pseudo-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 Sabatier effect when referring to negatives. Solarisation and pseudo-solarisation are quite distinct effects.

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.

Initially, the term solarisation was used to describe the effect observed in cases of extreme overexposure of the negative in the camera. Most likely, the effect was first observed in scenery photographs including the sun (e.q. sol, sun). The sun, instead of being the whitest spot in the image, turned black or grey. Minor White's photograph of a winter scene, The Black Sun 1955 was a result of the shutter of his camera freezing in the open position, resulting in partial overexposure. Ansel Adams created an image titled "Black Sun, Owens Valley, California (1939)" by overexposure solarisation.

The solarisation effect was already known to Daguerre and is one of the earliest known effects in photography. John William Draper was the first to call the overexposure effect solarisation. J.W.F. Herschel already observed the reversal of the image from negative to positive by extreme overexposure in 1840. L. Moser reported in 1843:"....., that the light in the camera obscura produces at first the well known negative image; with continued action of the light the image turns into a positive image.... and recently I have obtained in fact on occasion a third image which is negative". (in German)

The effect generated in the dark room was then called pseudo-solarisation. Spencer defines the Sabatier effect as: "Partial image reversal produced by brief exposure to white light of a partly developed silver halide image". Many other ways of chemical and actinic radiation "exposure" can be utilised for the partial image reversal. The use of chemicals for image reversal is also known as 'chemical fogging'.

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