Leon Warnerke

Wernerke's 1875 Roll-film camera

Warnerke is credited in 1875 with discovering the tanning effect of pyrogallic acid when used in the development of collodion, and an improvement of "dry" collodion emulsion, which he poured on a paper substrate in the form of a film layer.[4] He covered the smooth tissue paper successively with several layers of pure collodion and a solution of gum arabic, which through the formed a base for a photosensitive collodion or gelatin emulsion thick enough to be easily separated from the paper and permanently transferred to a moistened glass plate. The negative thus obtained could be used to make a positive, just like a glass negative.[5] This photosensitive material was produced by Warnerke's own company in sheets and rolls, from which rolls were cut into 100 photos for a single loading. Though, Warnerke achieved satisfactory results, the high production costs mitigated against greater than moderate commercial success.[6]

In 1875, Warnerke constructed a camera equipped with a special cassette for the film he produced in loads of 100 photos. A monorail bellows camera, it was one of the first cameras in the world that permitted taking such a large number of photos on a single load. Warnerke's construction was 9 years ahead of the 1884 invention of roll film by George W. Eastman and Fr. Hannibal Goodwin. Warnerke's camera had a small window of orange glass in the rear wall through which could be read the number of the negative's frame and position each precisely as the film was wound through; a device commonly used in later, modern cameras.

In 1881, Warnerke constructed another model of a photographic film camera, this time reduced to 40 negatives. The film used in this model was perforated with small holes at intervals of one shot. Because the sensitive gelatin emulsion had no paper backing, the orange window had to be replaced in this model with a tiny alarm bell triggered by an electrical contact being made through the perforations, which sounded after each frame moved to the appropriate point for taking a photo. The battery was inside the film roll. Warnerke's idea was later used by Eastman's company.

Warnerke's achievements include the sensitometer,[7] the first effective means of measuring plate speed, developed in 1880, which in the following year was recognized as a standard by a special commission and became the basis for standardisation in the field of photosensitive materials.[8] A reliable speed rating number for a given emulsion could be calculated against the known sensitivity of a collodion plate.[3] Warnerke's sensitometer was equipped with an energised phosphorescent block of calcium sulphide for his exposing source through a glass plate with 25 square fields of increasing density, so that the light absorption coefficient increased twice every three degrees, similar to the scale of the modern DIN system. Sensitivity in Warnerke degrees was a measure used in England almost until the end of the 19th century, but abandoned by 1920.

From 1889 Warnerke manufactured silver chloride gelatin papers for photographic printing.[3]