Dry gelatin process

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The dry gelatine process is a process from the early days of photography for the production of photographic negative material . In contrast to the previously customary wet collodion plates , the gelatine dry plates produced could also be stored before exposure and development.

Due to its advantages, especially the constant manufacturing quality and durability of the plates before recording and development, the gelatine process largely replaced the older collodion process for the production of so-called wet plates from 1850, especially in the amateur sector ; Due to the significantly higher production and purchase price, the wet collodion process remained widespread for a long time, especially in professional studio photography, where significantly more pictures were taken than by individual amateurs his assistant, which can still be seen in many old studio photos on the thumbprint of the assistant in a corner of the negative, where the latter held the glass plate while applying the emulsion.

The dry process itself was replaced from around 1880 by photographic film - initially paper , then celluloid , and later security film . Plate photography, whether wet or dry, remained up to around 1930, however, due to its generally greater light sensitivity, transparency quality and (since the glass negative was usually also larger than most film negatives) higher resolution compared to formats with flexible emulsion carriers, especially in professional photography Common in the 1950s.

Production and use

To produce dry plates, a gelatine- water emulsion was first created or potassium bromide (outdated: potassium bromide ) was dissolved in the water beforehand, i.e. an emulsion was correctly produced from a potassium bromide solution with gelatine. Then silver nitrate ( nitric acid silver ) was added to the liquid (in the dark) . This resulted in the formation of a suspension of water-insoluble silver bromide in gelatin, which was incorrectly called an emulsion or photo emulsion . The resulting silver bromide (outdated bromide silver ) was very finely distributed in it. The light sensitivity of this "emulsion" was not yet very high. However, if they were boiled for some time or treated with ammonia , their sensitivity increased considerably.

Since this orthochromatic "emulsion" is not sensitive to red light rays, the work, as well as subsequent development work in the " darkroom ", could be carried out under "red light" (ie not in the dark). This property, which was positive for production and processing, had a negative effect on the reproduction of human skin tones, which required make-up procedures for portraits .

When cooled, the boiled “emulsion” solidified, it could easily be finely divided, and the salts contained in it could also be removed with water. The remelted emulsion was applied to glass plates and allowed to solidify and dry thereon.

The high sensitivity of the gelatin dry plates was due to the formation of a highly sensitive silver bromide modification by boiling the emulsion; the former was discovered by Stas in 1874 .

advantages

The gelatine plates were distinguished from wet collodion plates by their durability, so that they could be comfortably carried when traveling; They were also six to ten times more sensitive than collodion plates and therefore allowed recordings with considerably shorter exposure times, including snapshots. They could also be made in stock for the trade, so that the amateur could avoid the tedious self-preparation of the negative material. Thus, they have given an extraordinary boost to amateur and amateur photography and its application in art and science.

History and Development

As early as 1866, the Austrian doctor and politician Norbert Pfretzschner senior, together with the Innsbruck chemistry professor Heinrich Hlasiwetz , succeeded in developing drying plates, which then also received a silver medal at the 1869 photography exhibition in Hamburg. However, this invention was not used industrially by Pfretzschner.

The gelatin process was developed by the British doctor Richard Leach Maddox as a by-product of bacteriological research around 1871; he published his results on September 8, 1871 in the British Journal of Photography . His method, which is still very light-insensitive , was improved by John Burgess and Richard Kennett . Photographic emulsions are based on the basic principle of embedded silver bromide in a gelatin layer .

In 1878 Charles Bennet succeeded in increasing the sensitivity of the gelatine process to wet plates by a factor of ten by producing the bromide silver gelatine with an excess of potassium bromide ( chemical sensitization ). This enabled snapshots with exposure times of a few fractions of a second. "From 1880 to 1882, Obernetter worked on improving the drying plates and with color collotype printing, and he also invented a process to produce a second negative of any size from a negative in the camera himself by means of development."

See also

literature

  • Josef Maria Eder : Detailed handbook of photography. Volume 3: Photography with silver bromide gelatine and silver chloride gelatine. Part 1: The manufacture of photographic plates, films and papers and their mechanical processing. Revised by Fritz Wentzel. 6th, completely revised and increased edition. Knapp, Halle (Saale) 1930.
  • Josef Maria Eder: Detailed handbook of photography. Booklet 9 = Volume 3, Booklet 1: The basis of photography with gelatin emulsions. 5th, increased and improved edition. Knapp, Halle (Saale) 1902.
  • Arthur von Hübl : The development of the photographic silver bromide gelatin plate with doubtful correct exposure. 4th edition. Knapp, Halle (Saale) 1918.

Web links

Individual evidence

  1. ^ Meyers Großes Konversations-Lexikon , Volume 14, Leipzig 1908, p. 867; online via Zeno.org