Like most inventions, Niépce's required a lot of experimenting before he found a way to successfully create pictures using sunlight.
He had to try different materials to capture the image on. Through many trials with paper, glass, and stones, Niépce learned that metal produced the best result.
He also had to find substances that reacted to sunlight to create the image on the metal plate. He painted the plate, made of a metal called pewter, with an asphalt-like paste. He then put the plate into a camera obscura, a very early version of the camera that looked like a box with a lens on one side.
The plate stayed inside the camera obscura for at least eight hours, while the parts of the paste struck by the sunlight began to harden. He then washed the soft parts of the asphalt-like substance off the plate with lavender oil.
What remained is the First Photograph captured on a metal plate.