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During his travel to England, Niépce had met, in Paris, Louis Jacques Mande Daguerre, painter and decor designer that had a reputation as camera obscura specialist. Hoping to shorten the exposure time of his process, Niépce decided in 1829, to associate Daguerre to his research to build a camera obscura giving brighter images . This association did not bring any noticable progress to the bitumen process, on the other hand, the two partners discovered new photographic processes using as photosensitive agents : tree resins and the residue of lavender oil distillation . The exposure time went down to about 8 hours in the sun .
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> Principle and technique : the PHYSAUTOTYPE
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The photosensitive agent of this process fine tuned by Niépce and Daguerre in 1832 was theresidue of lavender oil distillation.
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> Niepce and Daguerre obtained this residue evaporating lavender oil by heating it until they got a dry product . Submitted to heat lavender oil takes a a yellow hue that intensify with the elimination of the volatile stuff .
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> After distillation , only a dark brown tar dessicated by heat is left becoming hard and brittle.
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> Niépce and Daguerre would then dissolved a small amount of this tar in alcohol then poured the solution on a well polished silver plate.
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> After the alcohol evaporation, a uniform white deposit remained on the plate . The thus prepared plate was exposed to light in the camera obscura (for about 7 to 8 hours).
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> After exposure ,the plate was put upside down above a tray holding oil of white petroleum (something like kerosene) The fumes of this kerosene were sufficient to develop the image without any further treatment .
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This process gives directly positive images since the white deposit remains on the plate, at places that were touched by light, at the time the kerosene fumes render transparent the zones that were not illuminated. However, with the effect of reflexions on the metal appearing at places where the white deposit has become transparent, images can be seen as positive or negative.
> See the first reconstitution of "La table servie" (the set table) in Niépce's House |
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