Dry plate

The dry gelatin method is a method from the early days of photography for the production of photographic negative materials. Generated gelatin dry plates were in contrast to the above conventional wet collodion plates before exposure and development storable.

Production and use

(: Potassium bromide obsolete) dissolved so properly made an emulsion of a potassium bromide solution with gelatin initially a gelatin -water emulsion to produce dry plates was produced or in the water before potassium bromide. Then you put the liquid ( in the dark) silver nitrate ( nitrate of silver ) to. This results in a suspension of water-insoluble silver bromide formed in gelatin, this mass was erroneously called further emulsion or photo emulsion. In it, the resulting silver bromide (deprecated bromide ) was very finely distributed. The photosensitivity of these " emulsion " but was not very large. However, they cooked some time, or they were treated with ammonia, so took their sensitivity to very significant.

Since these orthochromatic " emulsion " against red light beams is not sensitive, the work could, just as subsequent development work in the " darkroom " in " red light" (ie, not in the dark ) are performed. But these for the production and processing positive property had a negative impact on the image of human skin tones, which make-up procedures required in portraits.

Chilled froze the cooked " emulsion ", she could easily be finely divided, also were able to be located in their salts are removed by water. The remelted emulsion was applied on glass plates and allowed to solidify and dry it.

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

Benefits

The gelatin plates were characterized with respect to wet collodion plates by their durability from, so they can be easily carried on the road; they are, moreover, were six to ten times more sensitive than collodion plates and therefore allowed recordings with significantly shorter exposure times, including snapshots. They could also be made for trading on stock so that the amateur could handle the painstaking self- preparation of the negative material. Folgemäß they have the amateur and lover of photography and the application given the same in art and science expanded greatly.

History and Development

In 1866 succeeded the Austrian physician and politician Norbert Pfretzschner senior to develop, together with the Innsbruck chemistry professor Henry Hlasiwetz dry plates, which then also in 1869 the Photographic Exhibition in Hamburg received a silver medal. This invention was not used industrially Pfretzschner.

The gelatin process was developed by the British physician Richard Leach Maddox as a by- product of bacteriological research 1871; He published his results on September 8, 1871 the British Journal of Photography. Its still very light insensitive method was improved by John Burgess and Richard Kennett. According to the basic principle embedded in a layer of gelatin silver bromide photographic emulsions are composed to this day.

Charles Bennet succeeded in 1878 to increase the sensitivity of the gelatin process compared to wet plates by a factor of ten by the Bromsilbergelatine with an excess of potassium bromide produced (chemical sensitization). This snapshots have been possible with exposure times of a few fractions of a second.

The gelatin process displaces the collodion process largely from 1850; it was even from about 1880 through the photographic film - first paper, then peeled celluloid and later safety film.

Yet " from 1880 to 1882 to Obernetter dealt with the improvement of dry plates and with the colors light pressure, he also invented a method to produce a negative in the camera itself an arbitrarily large negative second directly by means of evolution. "