Albumen Paper:

Paper coated with a mixture of albumen, potassium bromide and acetic acid, and once dry made sensitive to light with silver nitrate. It was used to obtain a positive image, the colour of weak coffee, after being exposed to the sun in contact with the negative obtained from a collodion wet plate.


American name (collodion positive on glass in Britain) of a variety of collodion wet plate, obtained by underexposing a glass plate with its front covered by a photo-sensitized emulsion and painting the other side black--or covering it with a piece of black cardboard or cloth--in order to achieve the effect of a positive image.


Photographic procedure invented by Henry Fox Talbot. It consists in treating fine writing paper first with a silver nitrate solution and then with a potassium iodide solution--which produces silver iodide--, and finally with a mixture of Gallic and acetic acids and silver nitrate, called gallo-nitrate of silver. A permanent but negative image was developed with gallo-nitrate and fixed with potassium bromide, which turned positive on contact with paper sensitized by sodium chloride and silver nitrate. In order to reduce copying time, the negative was run through wax or oil, which made it more transparent.

Camera Obscura:

An enclosure or box with blackened interior walls, in one of which there is a small circular orifice that lets the light in, thus projecting onto the opposite wall the inverted image of exterior objects. The optical principle behind it goes back to Aristotle, who pointed out that the smaller the orifice the clearer the projected image. Around 1550 a bi-convex lens was added to the orifice, which greatly improved the image. In 1558, in his book Magia naturalis, Giovanni Battista della Porta recommended the use of the camera as an aid for drawing, and in the mid-seventeenth century portable camerae obscurae began to be manufactured.

Cartes de Visite:

Multiple positive copies (9cm x 5cm) obtained from a glass negative that was exposed in a camera of between four and twelve lenses. They were printed by contact, cut and pasted on thin cardboard.

Collodion Wet Plate:

A procedure that consisted in painting a glass plate with potassium iodide and collodion--a solution of nitrocellulose in alcohol and ether--and then plunging it for two minutes in silver nitrate. The plate was exposed wet (hence the name) and developed in Gallic acid, while the image was fixed by sodium hyposulfite.


Single positive image, registered on a copper plate that was covered by a thin layer of highly polished silver and then made sensitive to light by fumes of iodine. Exposed in a camera, it was developed by mercury vapour. The first fixing agent was sodium chloride, which was quickly replaced by sodium hyposulfite. At first, the process required exposures of 20 to 30 minutes, but optical and chemical improvements introduced at the beginning of the 1840s shortened exposure time to fractions of a second. A daguerreotype image has its left and right sides inverted with respect to the model, in a manner similar to what is seen on a mirror, and changes when rotated in front of the eyes, being perceived sometimes as a positive, full and contrasted and others as a negative. This characteristic is particular to daguerreotypes and enables to identify them. Properly insulated from the exterior, daguerreotypes are practically unalterable, but contact with the air oxidizes and deteriorates them. As the image is extremely fragile, it should not be touched: attempts to clean the surface of a daguerreotype with a piece of cloth have frequently resulted in serious damage or the irretrievable loss of the image. For protection, they were covered with glass, which was separated from the image by a passepartout (called mat by Americans) and pasted on hard cardboard with strips of gummed paper that sealed the edges and left the piece completely encapsulated.


A procedure also known as melanotype (and tintype in America). It is a variant of the wet collodion plates: instead of the glass used for ambrotypes, it required black enameled tin-plate (as in actual fact the plates were made of iron, tintype is a misnomer). Once developed and fixed, the resultant image was positive.


The name given by Niepce to the first photograph ever made, which he obtained in 1826 after covering a pewter plate with an asphalt emulsion called bitumen of Judea. He exposed the plate in a camera obscura for eight hours and then washed the unexposed bitumen off with lavender oil and turpentine, thus producing a permanent image.


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