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Johann Schulze was a German physicist who darkened silver salts with the use of light.
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Carl Scheele, a swedish chemist, found out that use of chemical can make color of silver salts permanent.
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Heliography, meaning “of the sun”, was invented around 1824 to capture the permanent image. In the process of making heliography, Niépce used light-sensitive varnishes and silver chloride, but the images were turned out to be negative. Later, he produced a solution of bitumen of Judea, a type of asphalt, which he succeeded in making a positive image. Heliography was not popular because it took eight hours to expose and it was hard to make many copies of the images.
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The first successful photograph after eight hours of exposure
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the partnership with Daguerre did not last long when Niépce died in 1833.
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In the late 1830s, Daguerre invented the daguerreotype which was the develop form of heliography. The daguerreotype was the image that did not fade and took less than thirty minutes to expose.
