- He left St. Petersburg, Russia, in 1870 for London, where he started a photochemical company. Having invented a film-roll holder in 1875, he also experimented with the production of silver bromide collodion emulsion, producing silver bromide films on gelatinized paper and becoming the first to use "stripping films" with a roller dark-slide. In 1889 Warnerke produced gelatin silver chloride paper, calling it "the printing process of the future." He devised the sensitometer in 1880 - the first practical device for measuring exposures - and in 1885 introduced and patented a negative paper coated on both sides. Warnerke lectured frequently before the photographic societies of England, France, Belgium and Germany. He returned to St. Petersburg and founded a photographic firm there in 1880 as well as a technical journal, then retired to Geneva around 1898-99.