There are a variety of chemical compounds that are photosensitive, but the most widely used from the earliest days of photography has been the conversion of silver halides, AgX (X = Cl, Br, I), to produce metallic Ag and X 2. The basic steps are outlined below, and this will be followed by some information on variations in the process.Įxposure: the fundamental chemical process

Once these materials were in hand, the taking of a photographic image could be divided roughly into four steps, although not all steps were used in all processes.

In the earliest days, the photographer had not only to make and process an image but also had to create the photographic papers and plates to be used. Photography involves several distinct steps. True color photography is a complicated technology but it still relies on the same fundamental photochemical reaction. These photographs can be modified by chemical means to change the color of the image in a a process called toning that we will discuss later once the fundamentals are described. The earliest photographic images were created with a single color process that, for simplicity, we will label as black and white photography, although many of he early images will be distinctly brown or perhaps blue. Photochemical processes can be very different from the reactions that occur by simply heating a reaction mixture and are dependent on the wavelength of light employed. This overall process falls under the category of photochemistry, and shining light on chemical substances is a routine technique by which chemists add energy to a system to make a reaction occur. In order for photography to work, the light reflecting from an scene must be focused on photosensitive substance that consequently undergoes a chemical reaction in proportion to the amount of light that strikes it. While film photography is being replaced by the digital realm, film photography and classical photographic printmaking still offers the artist a medium that has tremendous flexibility and opportunities for creativity. Digital photography is becoming an increasingly important medium, and it also relies on light reflecting off of an object to capture its image, but that process is distinctly different, involving the focusing of light onto a detector that creates an array of electrical signals from the received light and records those signals as intensities and wavelengths in digital form. It is those chemical processes that will be the focus this page. The camera obscura had been known for centuries and was employed by artist to help transfer projected images into drawings, but it wasn't until the early 1800s that cameras began to be used for focussing light onto photosensitive chemical compounds so that the images could be recorded. The word photography comes from the combination of the Greek words drawing and light, and signifies the creation of an image with light. Photos can be overexposed or underexposed, multiple images can be created and the color values changed through chemical processes. The limits of the photographic processes have been pushed to achieve a wide variety of artistic effects. But photography has been more than a method of recording events and people. Theis led inevitably to the impressionist movement and to ever increasing abstraction and surrealism. It has been argued that one of the most profound effects that the introduction of photography had on Art was to free up the artist to no longer be constrained as the conveyor of reality - rather the artist was now free to interpret a subject as he or she saw fit. Portraits became accessible to socioeconomic classes in ways not possible when the primary means of portraiture was to hire an artist to draw or paint the subject. The Civil War in the United States became one of the first historical events to be chronicled by photography as have all major historical events since that time. The development of photography has had a profound effect on society.

Camera obscura box, unknown illustrator, 18th century, Public domain, via Wikimedia Commons.

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