It is quite simple: the photographic paper reveals an image when exposed to light.
By adding a light-sensitive layer, called the emulsion, to a base of fiber or resin, the paper becomes sensitive to light. In the past, the emulsion was usually based on silver salts.
The British inventor Thomas Wedgewood first observed this phenomenon in 1802.
Yet, he could only capture shadows on paper coated with silver chloride and he died before he could develop it further. After his death, another Briton, William Fox Talbot improved the emulsion and added a developing agent.
William Fox Talbot is the inventor of the calotype process.
The calotype process consists of placing a light-sensitive paper inside a camera obscure. Once the light enters through the pinhole, a negative appears on the paper. To get a positive, the negative is placed onto another piece of photographic paper. Through a process called contact printing, the final positive image is obtained.
Back in the days, the process was very slow and the photographs were extremely fragile. By adding the use of developing agents, which wash off the silver layer, photos would last longer. With time, technology continued to progress, the images became clearer and eventually in colors.
Today’s photographic paper
Nowadays, there are two major types of the photographic paper base. One is the fiber (FB), sometimes called baryta, and the other is the resin (RC) that first appeared in the 1960s.
The vast majority of pictures (Prints) in the IMS archives are FB and RC prints.
Besides the variety of bases, there is an even more diverse selection of emulsions.
Most of the photographs in the archives are made with silver bromide and silver chloride compound suspended in gelatin.
The various compounds produce distinct qualities in the final image. In fact, the emulsions and bases affect the contrast, the tonal range, and the brightness of the picture.
In photography, other elements have been used to create emulsions, including platinum and uranium. However, none ever achieved widespread use.
Almost all prints in our collection are black and white silver prints: the color prints were a rarity because of being hard to produce. They became popular from the early ’60s when Kodak industrialized the process.
The negative-positive photography process was dominant in the past and today there are several positive-positive systems in use. One that was abandoned was the Ilfochrome process. It discontinued in 2012 because of the decline in demand with the rise of digital photography.
One that survived and is back in style today is the Polaroid.
The Polaroid Company invented its famous Polaroid camera that would develop pictures instantly, back in 1947. Polaroid is making a comeback thanks to the feeling of nostalgia linked to owning a physical print.
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