What experiment promoted the birth of photography?

In addition, Herschel also explored adhesives. 1839 he did an experiment: put a piece of glass under a pot of silver chloride solution and let the silver chloride solution slowly deposit on the glass plate. This experiment provided beneficial enlightenment for later researchers. Later, he suggested that Talbot use hypo instead of salt as fixing agent to fix the image. These experiments and ideas promoted the birth of photography.