1825-1829 > INVENTION OF PHOTOGRAPHY   • 1816-1818  • 1819-1824

n 1824, he put lithographic stones, coated with bitumen ,at the back of a camera obscura and obtains for the first time a fixed image of a landscape. This required an extremely long exposure time , in broad daylight , of a few days. Starting in 1825, he used regularly copper as a base, then tin in 1826, and realised etched images.

n 1827, Niépce went to England where he found his brother dying, unable to show any improvement to the engine . He realisesd then that they would never get any profit from this invention in which they had invested so much hope . After having vainly tried to get the attention of the Société Royale to his reproduction process of images that he calls Heliography , Niépce came back to France and relentlessly worked to improve his invention . In 1828 he found a new method that led to superior quality images with half-tones . Using as a base polished silver and letting interact iodine vapours on the bitumen image he obtained genuine photographs in black and white on the metal plate .The preciseness of these images is amazing for the time .The exposure time is still many days in broad sunlight .

> Principle and technique of HELIOGRAPHY with the camera obscura
The photosensitive agent is Judea bitumen .
It is a sort of natural tar known from ancient time. People in antiquity used to collect it from the Dead Sea surface ( in greek Asphaltite lake ) where it keeps surfacing continually from the bottom of the sea. It was used by the Egyptians to embalm mummies, to caulk ships or even to make terrace works in Babylon. In the 19th century, people already knew how to extract that tar from bituminous rocks and as a matter of fact the bitumen used by Niépce did not come from Judea.

> See our video about bitumen varnish  
> See our video about revealing the image  
> See our video about iodine treatment  
Extracts from the movie "Magie de l'image" - Download time : up to 4 minutes

1 - Obtention of a Judea bitumen image :

> Niépce dissolved powdered Judea bitumen in lavender oil.

> Then he spread this solution in a very thin layer on a base ( glass , stone , copper , tin , silver).

> With a hot drying process he got a shiny varnish with a cherry red color.

> He would then expose the varnished plate in a camera obscura (here a slide projection).

> After exposure, there was no visible image. Niépce would dip the plate in a diluted lavender oil bath that would dissolve the bitumen parts that had not been exposed or very little to light.

> The resulting image, seen with a normal incidence, was negative.
The exposure time in a camera obscura was quite a few days in broad sunlight.

2 - Utilization of a Judea bitumen image :

> To get a positive image , Niépce used the image in two ways : without any further processing under the condition to make this image with an extremely thin layer of varnish with a slight underexposure ( from 1827 on ). In this case the varnish was mat and by reflection , with a low angled light and in a dark place , the image would appear as a positive.

> Submitting the silver plate to iodine vapors to get a positive image (from 1828 to 1831 ) Niépce would place it in a box with iodine crystals that evaporated spontaneously.

> Within a few minutes the iodine fumes oxydized the silver insufficiently protected by the varnish. This created a layer of silver iodide on the metal surface, which once the varnish was eliminated, would blacken under the action of light.

> He would get a posiive image.