Negative-positive technique
William Henry Fox Talbot was an English gentleman of means. Whilst on a grand tour of Europe, he considered the possibility of permanently imprinting the charming images obtained with his small camera obscura. Upon his return to England, Talbot experimented by sensitising a piece of writing paper and exposing it for over an hour. The fragile lilac-tinted sheet is acclaimed today as the world’s first negative. Thus the negative-positive technique was born, making possible the creation of multiple prints from a single negative. In1839 Talbot published all the technical details required to duplicate his technique. At about this time the British astronomer Sir John Herschel made the vital discovery that sodium thiosulfate (hypo) was the best fixing agent to make photographs permanent.