Other Free Encyclopedias » Online Encyclopedia » Encyclopedia - Featured Articles » Contributed Topics from P-T » The Technical Evolution of Photography in the 19th Century - Concept and First Attempts, Joseph Nicephore Niépce, Louis Jacques Mandé Daguerre, Daguerreotype, Photography on Paper

Gelatin Emulsions and the Modern Era

plates collodion time process

It may seem out of place to call the last quarter of the 19th century the modern era of photography. However, the introduction and eventual acceptance of gelatin emulsion plates, papers, and flexible films in this period became a technology that was not challenged until digital imaging appeared at the end of the 20th century. Looking back from a 21st-century perspective, we might more appropriately call the late 1800s the last era of photography.

The complicated evolution of research, development, and manufacturing of silver gelatin photographic materials in the latter quarter of the 19th century is filled with simultaneous invention, lawsuits, and countersuits. Chronicling the history is beyond the scope of this essay, but what follows presents the essential progression.

The invention of emulsion plates was primarily English and began with collodion emulsions of the 1850s. In 1865 G. Wharton Simpson made printed images on paper coated with a collodion chloride emulsion. Soon after this, leptographic paper coated with a collodion chloride emulsion was manufactured by Laurent and Jose Martinez-Sanchez in Madrid. An innovation introduced specifically for collodion emulsions was the use of a baryta coating applied to the paper support as a smooth, white barrier layer. Leptographic paper was made until 1870 with limited success, but baryta papers reappeared several years later and were eventually used throughout the 20th century for all photographic papers.

In England W. B. Bolton and B. J. Sayce introduced a collodion emulsion for negative plates in 1864 that was based on bromides rather than iodides. These were nearly as sensitive as wet collodion plates and were processed with an alkaline developer. The use of bromides and of alkaline development was to become the key to making fast plates with gelatin emulsions. Collodion emulsion plates remained the territory of advanced amateurs for the next 20 years.

Based on the earlier experimental work of W. H. Harrison, Dr. Richard Leach Maddox added silver nitrate to a warm gelatin solution bearing some cadmium bromide and then coated some glass plates with the emulsion. After exposing the plates in the camera, Maddox developed them with pyrogallic acid and some silver. The process used with these plates was slower than the wet collodion process but was the first serious attempt at making a gelatin emulsion. Maddox’s silver bromide gelatin emulsion process was published in the British Journal of Photography in 1871.

Additional experiments in the early 1870s were continued by John Burgess, who used pyro developer in an alkaline state. The problem with the Burgess emulsion was that although it contained the necessary silver bromide, it was also affected adversely with potassium nitrate, a by-product of the technique. Removing the unwanted compound was first accomplished by J. Johnson, who allowed his gelatin emulsion to dry into thin sheets called pellicles. He then cut them into small pieces and washed them in cool water. After washing, the sensitive gelatin was dried in darkness and packaged. These pellicles could be stored and rehydrated for coating at a later time. Richard Kennett patented a similar product of washed sensitive pellicles in 1873 and was selling both the pellicle and the precoated gelatin plates by 1876. The English market for gelatin plates was growing steadily but did not fully topple collodion technology until the mid-1880s.

Gelatin emulsion plates were a hard sell to professional photographers who were used to getting excellent results with the wet collodion process. The early gelatin plates were met with limited interest and limited commercial success. The discovery that changed everything was observed when the gelatin pellicle was rehydrated and the emulsion was melted. The longer the emulsion was heated, the more sensitive it became. The cause, called ripening, was first identified by Sir Joseph Wilson Swan in 1877 and was a trade secret until revealed in 1878 by Charles Bennett, who also observed the phenomenon. Bennett continued his experiments by keeping the emulsion hot for days.

A year later George Mansfield suggested ripening the emulsion at a higher temperature over a period of minutes, a method generally adopted by all those who continued research in this area. By 1879 gelatin emulsions were ripened by heat and then allowed to set to a firm jelly. The emulsion was squeezed through a mesh to produce noodles that were washed in cool water to remove the unwanted nitrate. The washed noodles were then drained and remelted with some additional gelatin and applied, while hot, onto glass plates by hand under dim, red light. Coated plates were then placed on marble leveling tables until the gelatin set to a stiff jelly, at which point they were taken to a dark drying room and packed in boxes. This was the way all commercial plates were made until the development of automated equipment in the mid-1880s.

Gelatin plates, also called dry plates, were being manufactured by hand on a much larger scale by 1880. Interest and acceptance by both amateur and professional was much slower in the United States than in England and the rest of Europe. The English photographic journals at this time were beginning to include more articles on the gelatin process than collodion, and these, in turn, were being reprinted in the American journals. Some American professionals began using the new plates with mixed results, and they published their findings.

In 1880 the Photographers Association of America appointed a committee to investigate the new technology of gelatin plates. The quality of commercial plates varied considerably, but the plates had great potential in skilled hands. Many of the problems photographers had with these plates were due to increased sensitivity. Fogging, more often than not, was caused by overexposure in the camera or poor darkroom conditions that had little effect on the slower collodion plates.

As interest grew, more plate manufacturers appeared on the American horizon, and more professionals began taking the risk of changing their systems from wet to dry. The prices of plates were decreasing, and interest was growing. At the same time, all of the manufacturers of cameras and associated equipment were targeting a new generation of amateurs who could make images at any time without the skills that were previously necessary.

Gelatin plates could be relied upon at any time and developed later at a more convenient location. When plate-coating machines became a reality, the price of plates was reduced enough for the commercial photographer to adopt plates for their work as well. It can be assumed that most commercial photographers in America were using gelatin plates for both exterior and studio portraiture by 1885.

The popular developers for these early plates were alkaline solutions of pyrogallic acid or ferrous oxalate. Within a few years, hydroquinone was also used, followed by metol and a combination of the two chemicals, commonly called MQ developer. Developing powders were available in boxes of premea-sured glass tubes.

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