John Herschel is father of the cyanotype. But he also made improvements to other photographic processes. Long before cyanotype, Herschel discovered sodium thiosulfate to be a solvent of silver halides in 1819. He then informed William Henry Fox Talbot and Louis Daguerre – inventor of the daguerreotype – that this “hyposulphite of soda” could be used as a fixer to make light-sensitive images permanent. Sir Herschel presented his groundbreaking research to the Royal Society on March 1839 and January 1840.