Making the Image Permanent
Scientists had known for some time that certain silver compounds, then called silver salts and now named silver halides, would turn black when exposed to light. In England, Thomas Wedgwood, son of the famous potter, experimented with one of these silver halides, silver nitrate, to produce silhouettes. The pictures, however, were not permanent and turned black unless stored in the dark.
1.Niepce In the early 19th century Joseph-Nicephore Niepce of France began to experiment with a then novel graphic arts printing method called lithography. His work led him to further experiments using bitumen, a resinous substance, and oil of lavender. Niepce developed a process whereby he could permanently capture the image of a camera obscura. In 1827 he made the world's first surviving photograph from the window of a country home in France. It required an exposure, in bright sunlight, of eight hours.
2.Daguerre Meanwhile, Daguerre was experimenting with silver-iodide images. Hearing of Niepce's work, he contacted him, and in 1829 they became partners. During the next few years Daguerre, with Niepce's help, worked out the process that came to be known as daguerreotypy. It was a complicated procedure that demanded considerable skill. A silver-coated sheet of copper was sensitized by treatment with iodine vapor, forming a coating of light-sensitive silver iodide. The daguerreotype plate was exposed in the camera and then developed in mercury fumes at temperatures of about 120 degrees F (50 degrees C). The exposed areas absorbed mercury atoms and highlighted the image. Finally, the image was fixed by washing it in hypo. The daguerreotype's silver image was capable of rendering exquisitely fine detail. It was a single-image process, however--each exposure produced only one picture, incapable of reproduction. Furthermore, the process required exposures of up to several minutes even in bright sunlight, thus constraining its subjects to absolute motionlessness. In spite of this, the process immediately became popular, particularly for portraiture. Daguerreotypy rapidly developed into a thriving business in England and the United States. Superb portraits were made by such daguerreotypists as Albert Sands Southworth and Josiah Johnson Hawes in Boston. The French excelled in landscapes and cityscapes. In 1840 a much faster lens was designed by the Hungarian Jozsef Petzval and manufactured by Peter Voigtlander in Austria. At about the same time a method was discovered that increased considerably the light sensitivity of the daguerreotype plate. This method involved a second fuming with chlorine or bromine before exposure.
3.TalbotIn England William Henry Fox Talbot had developed his own method of photography at about the same time that Daguerre was inventing the daguerreotype. Talbot impregnated paper with silver nitrate or silver chloride. When exposed in a camera, the sensitized paper turned black where light struck it, creating a negative image of the subject. This was made permanent by fixing with hypo. To achieve a positive image, a contact print could be made by placing the negative over a second piece of sensitized paper and exposing the combination to bright light. Talbot's "photogenic drawings," as he called them, lacked the daguerreotype's sharp detail and brilliance but offered the great advantage that from one negative a large number of positive prints could be made. His process, known as the calotype, and later talbotype, process, was at first less popular than the daguerreotype. Most later methods of photography, however, have evolved from Talbot's work. His was the first negative-positive process.
4.ArcherIn 1851 F. Scott Archer of England made public his wet-collodion process, in which he used a glass plate coated with collodion as a base for light-sensitive silver halides. His procedure, requiring seven steps, was only slightly less complicated than the daguerreotype process, but it was considerably less expensive. It also produced a negative that was much sharper than that of the calotype method. Soon the wet-collodion process had supplanted both the older techniques as the most widely used process of photography. A major inconvenience of the wet-collodion method was the fact that the plate was light-sensitive only as long as it remained wet; after it dried it lost its sensitivity. Thus plates had to be used almost immediately after preparation. Since these plates could not be prepared and stockpiled in advance, a portable darkroom, in the form of a tent, wagon, or railway car, for instance, had to accompany the camera wherever it went.