READING PASSAGE 1

Answer Questions 1-13, which are based on the text below.

Early Photographic Processes

The decades following photography's experimental beginnings in the 1820s and the public availability of a practical photographic process from 1839 were characterized by the introduction of a wide number of photographic processes. The following are a few of the most significant.

Announced in Paris in 1839, the daguerreotype was the first publicly available photographic process. The daguerreotype image was created on a silvered metal plate exposed to iodine fumes, forming a light-sensitive surface of silver iodide. Development was achieved by exposing the plate to fumes of heated mercury and then fixing the image in a salt solution. The daguerreotype produced remarkably sharp pictures, but unlike competing processes, each daguerreotype was unique. This proved to be its major drawback, compared to other processes from which unlimited copies could be made.

One of the oldest and longest surviving photographic processes, the cyanotype or blueprint, was invented by Sir John Herschel in 1840, using a mixture of ferric ammonium citrate and potassium ferricyanide to produce a light sensitive paper. As a relatively simple process to prepare and manipulate - it required no development or fixing other than washing - it was popular among amateurs throughout the nineteenth century and has also been widely used by engineers and architects for reproducing technical drawings (blueprints).

William Henry Fox Talbot's calotype process, the first practical negative-positive photographic process, was patented by him in 1841. A sheet of good quality paper was first treated with light-sensitive silver compounds before exposure in the camera. This produced an image in reverse, known as a negative, which was then developed in gallo-nitrate of silver and fixed. This concept of photography, allowing the production of an unlimited number of prints from a single image, has formed the basis of photographic practice until recently, when it started being challenged by digital imagery. The calotype negative was the subject of many refinements in the 1840s and 50s, and it was common practice for photographers to apply heated wax in order to increase printing transparency and lessen the visibility of the paper fibres.

Frederick Scott Archer's wet collodion process, announced in 1851, became the standard photographic process for both amateurs and professionals from the mid-1850s until the early 1880s. The process proved immediately popular, and within a decade had superseded both the daguerreotype and the calotype processes. To prepare the negative for exposure, a sheet of glass was coated with a solution of iodised collodion (a syrupy liquid composed of soluble gun-cotton, ether and alcohol) and then made light-sensitive by immersion in a bath of silver nitrate. Known as a wet process because the glass negative required sensitising, exposing and processing while the chemicals were still damp, it required significant skill to manipulate, but produced a negative of unsurpassed sharpness and a broad tonal range.

The albumen print, announced by the French photographer and publisher Louis-Desire Blanquart-Evrard in 1850, was the most widespread print medium in use between the mid-1850s and the 1890s. While the printing process was chemically similar to an earlier process which was called the 'salted paper process', the albumen print was generally distinguishable by the glossy sheen imparted by a preliminary sizing of the paper with albumen (egg white) and salt. After the albumen coating had been applied, the paper was made light sensitive by the addition of silver nitrate, and printed in contact with the negative. The fixed print could then be toned to create a wide variety of colours, ranging from purple-black to a rich chocolate brown. Although it continued to be used well into the twentieth century, its popularity declined after the mid-1890s, in favour of a variety of manufactured papers.

The fact that all silver-based photographic images tended to fade was a source of concern from the earliest days of photography, and considerable research was carried out in attempts to produce permanent images. Perhaps the most successful of these was the carbon process. First patented by A L Poitevin in 1855, the process utilised the fact that gelatin mixed with an alkaline bichromate becomes insoluble when exposed to light. When printing from a negative, those parts of the image representing shadow tones were hardened by the exposure to light, while light areas, protected from exposure, remained unhardened and could be subsequently washed away. Carbon and other pigments could be used as colouring agents to obtain an almost unlimited range of tones in the final image. Because the process does not employ compounds derived from silver, the resulting image is less likely to fade and was widely used in book illustration in the 1870s and 1880s.