Far across the courtyard, behind the dovecote, you can make out a pear tree with a gap in its foliage. Everything was already there. That makes photographic film sound a bit like a Flintstones relic, what with cameras going digital and darkrooms giving way to computers. In the late 1980s, Belloni helped elucidate the fundamental chemistry of film developing.
Film is basically a lot of silver halide crystals suspended in gelatin on a plastic backing.
When a camera's shutter opens, light photons stream through the lens, fall on some of the crystals, and dislodge electrons from the halide ions. Some of the electrons glom onto nearby ions of silver, converting them to neutral atoms. The atoms then cluster together, forming a tiny black speck of metallic silver on each exposed crystal. Millions of such specks form the image. To make a positive print, you shine a light through the negative onto a paper covered with the same kind of film emulsion, and then develop that.