Physautotype
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The physautotype (from French) was a photographic process, invented in the course of his investigation of heliography, by Joseph Nicéphore Niépce and Louis Jacques Mandé Daguerre[2] in 1832, in which images were produced by the use of lavender oil residue dissolved in alcohol as the photographic agent.[3][4] The solution was coated onto a silver or glass plate and allowed to dry, after which it had a powdery white appearance.[citation needed] The plate was then exposed in a camera obscura for about 8 hours and developed with petroleum-based spirit vapors,[3] which caused the least strongly exposed areas to become proportionally more transparent, creating a photographic image that was positive when viewed against a darker background.
On his way to England, Niépce met in Paris with Louis Daguerre, who had a reputation as camera obscura specialist. Hoping to shorten the exposure time of his bitumen process, Niépce decided in 1829, to associate Daguerre to his research. This association did not bring any noticeable progress to the bitumen process; however, the two partners discovered new photographic processes using as photosensitive agents tree resins and the residue of lavender oil distillation. With those, the exposure time went down to about 8 hours in the sun.
Chemical principle
The resin is melted and a little portion of it is dissolved on alcohol. Then a silver plate, a glass plate or a mirror is coated with the solution and allowed to dry on a tray. Once it's completely dry, the alcohol evaporation leaves a residue of tiny dispersed resin particles that give the plate a white, blurry appearance.
When exposed to the sun, the exposed areas seem to polymerize[5] becoming insoluble, while the unexposed areas are still soluble. The plate is developed over a tray with spirits like kerosene and turpentine, which wash away the unexposed areas. The process lasts 5 to 10 minutes, and the solvent must never touch the plate. If left over the vapors for longer, the plate continues developing itself, with the final product of a clear plate with nothing on it.[6]
