The Sabattier effect, also known as pseudo-solarization (or pseudo-solarisation), 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. Solarization and pseudo-solarization are quite distinct effects. Over time, the "pseudo" has been dropped in many photographic darkroom circles and discussions, but the effect that is meant is the Sabattier effect and not the solarization by extreme overexposure (see below).
Initially, the term "solarization" was used to describe the effect observed in cases of extreme overexposure of the photographic film or plate in the camera.
The effect generated in the dark room was then called pseudo-solarization. Spencer defines the Sabattier 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'. Another usable definition is by Wijnekus & Wijnekus: If an exposed, incompletely developed, and washed, but not fixed film is given a second uniform exposure and developed again, a reversal of the original image may be obtained. The reversal may be partial or complete, depending on the relative magnitude of the first and second exposures.
The Pseudo-solarization effect was described in print by H. de la Blanchere in 1859 in L’Art du Photographe. It was described again in 1860 by L.M. Rutherford and C.A. Seely, separately, in successive issues of The American Journal of Photography, and in the same year by Count Schouwaloff in the French publication Cosmos. French scientist Armand Sabatier published 26 October 1860 a process of obtaining direct positives (referencing Count Schouwaloff and Poitevin), but according to the description, this process did not seem to have any connection with the Sabattier effect as no mentioning was made of any exposure of the collodion plates after development had started. The name of the author was erroneously spelled with double "t" and thus the effect is hence known as the Sabattier effect in most literature. Sabatier described correctly the phenomenon in 1862. However, Sabatier could not find an explanation for the phenomenon.
The effect was usually caused by accidentally exposing an exposed plate or film to light during developing. The artist Man Ray perfected the technique which was accidentally discovered the darkroom of fellow artist Lee Miller. It is evident from publications in the 19th century that this phenomenon was discovered many times by many photographers as it tends to occur whenever a light is switched on inadvertently in the darkroom while a film or print is being developed.
Whereas many photographic effects have been researched and explained in such a way that most researchers agree upon them, the Sabattier effect does not belong to that group. In general the following facts are accepted by the community of photographic researchers: