A term devised by Marcus Arelius Root for his variation of the wet-collodion process (see below) that produced a unique positive, silvery-white image on a dark glass plate (or a transparent plate that was painted black, or backed with dark velvet). Purposely under-exposed collodion plates were bathed in ferrous sulfate developer to produce the positive effect when viewed by reflected light (when viewed by transmitted light, ambrotypes are under-exposed negatives). Ambrotypes were packaged in special presentation cases in imitation daguerreotypes. The technique was not commonly used after the mid-1860's.

A nineteenth and early twentieth-century process for making positive prints in paper which is essentially a variation of Talbot's salted paper printing process (see below). As originally described by Louis Desire Blanquart-Evrard, table salt was beaten into egg white and the mixture spread on sheets of paper and allowed to dry. The treated paper was sensitized with silver nitrate and dried in the dark. Printing was by contact (see below) with a negative; long exposure to daylight was required since the image was completely printed out during the exposure, rather than being developed after exposure. Blanquart-Evrard found that paper coated with the albumen-salt mixture produced prints with an objectionable luster, and accordingly, recommended diluting the albumen about fifty-percent with salt water to produce prints similar in surface character to salted-paper prints (known as dilute albumen prints). By the late 1850's, however, manufacturers and photographers came to prefer lustruous prints and coated paper with the undiluted salted-albumen mixture; beginning in the mid-to-late 1860's paper was double coated in order to obtain an even higher gloss on the print surface. In the 1870's and even higher gloss was achieved by bathing processed albumen prints in a castile soap solution and passing them through heated and highly polished steel rollers. Since albumen prints fixed with chemical toning turned an unattractive brick red, the majority were processed in a toning bath after exposure to give them an acceptable hue. The procedure for the toning of albumen prints remained a highly individual preference for photographers well into the 1850's. Exhausted fixer was a popular toning bath for both salted paper and albumen prints during this time and produced a variety of tones from red, through sepia and bistre, to deep purple depending on the length of toning, which ranged from an hour or two to as long as two or three days. From the early-to-mid 1850's, the sepia-brown to purple-black of many albumen prints was achieved by bathing prints in sel d'or (a mixture of fixer and gold chloride), which had originally been employed to tone and improve the contrast of daguerreotypes. While both of these toners were effective in producing rich prints, they were often responsible for a pronounced yellowing and degrading of albumen prints over time. In 1855, James Waterhouse devised an improved method of toning which produced permanent prints when used with care. His toning bath of gold chloride and a mild alkali in an aqueous solution produced a variety of pleasing hues depending on the concentration of gold and the length of time the print remained in the toner. Lower concentrations of gold produced a sepia hue; higher concentrations gave purple to blue-black hues. Since the subsequent fixing bath altered the initial hue, experience and practice were necessary for exact and consistent results. This toning procedure became standard practice in the early 1860's.

"Autochrome" was the brand name of the first commercially marketed photographic color transparency process. Introduced in 1907 by the French inventors and manufacturers, Auguste and Louis Lumiere, the material was simple to use and was processed with the chemistry of black and white photography. The Plates were made by dusting starch grains dyed in the three additive primary colors (green, blue, and red) onto a glass plate, which formed a random pattern (called a reseau) of minute, translucent colored dots. These grains were then flattened under pressure and coated with a panchromatic emulsion. Exposure in the camera was made with the glass plate facing the lens (so that the light would pass through the dyed grains and then expose the film). The grains acted as filters, blocking some colors of the subject and passing others which the registered on the panchromatic film. After exposure the plate was developed as a black and white negative and then treated chemically to reverse the image onto a positive. The resulting black and white transparency selectively blocked or transmitted the colors of the starch grains in such a way as to make the image appear to be in full color when viewed by transmitted light or when projected onto a screen. Within a year or two of the introduction of Autochrome plates, several members of the Photo-secession, including Alfred Stieglitz, Edward Steichen, Alvin Langdon Coburn, and Frank Eugene experimented with, exhibited, and published their results with the new process.

A printing technique perfected by G.E. Rawling after 1904 from contributions by earlier experimenters. The basis of the technique is that gelatin is mixed with potassium bichromate (now called potassium dichromate) absorbs less water when exposed to light than when unexposed. When oil-based ink in applied to the print surface it adheres better to areas less saturated with water and thus results in the differentiation between blacks, whites, and intermediate grays. The bromoil technique itself was introduced around 1907 and allowed photographers to produce this lithographic matrix on enlargements made on specially manufactured silver bromide paper. Inks could be applied by roller or more expressively by a stiff-haired brush. Often the final print was a result of the transfer of the ink from the matrix to a final support.

A positive printing technique similar in its chemistry to gum printing (see below). The carbon print used not only lampblack for its colorant but also other pigments. Unlike gum prints, the carbon print material was manufactured (from the 1870's on)  because  the thickness of the coating needed to be carefully controlled. Contact exposure was through a positive transparency made from the original negative. Development was in water until the gelatin swelled at which time the exposed carbon tissue was pressed into contact with an ordinary sheet of paper for about five minutes and then the two were immersed in a tray of lukewarm water. After the unexposed gelatin of the original carbon tissue was dissolved away, the papers were separated and the image remained on the ordinary paper. The process was devised in order to increase the permanence of positive prints and still maintain a continuous and delicate tonal range.

The photographic process invented by William Henry Fox Talbot in September 1840, in which paper impregnated with silver iodide is sensitized by an aqueous solution containing silver nitrate, acetic acid, and gallic acid, exposed in the camera, and then developed as a negative with the same sensitizing solution. In his 1841 patent of the process, Talbot states that the negative is fixed in a saturated solution of potassium bromide. In his 1843 patent for improvements, he specifies an after treatment of the negative is a hot bath of sodium hyposulfite (known as sodium thiosulfite) to improve its whites and increase its permanence. Photographers soon discarded the potassium bromide bath and fixed their negatives directly in "hypo". Talbot's development of the latent image formed by short exposure in the camera- actually a type of image intensification and technically known later as "physical" development- was a great breakthrough in his attempt to make photographs with the camera. The negatives of Talbot's early photogenic drawing process (see below) were too thin and lacked sufficient contrast to produce acceptable positive prints. Not only did development of the calotype negative greatly increase the light sensitivity of the paper, it also produced negatives that were easily printed. Although Talbot mentioned developing prints after contact exposure to the paper negative, his preferred method was to employ his photogenic drawing paper (salted paper) as the positive print material. Hot wax was often applied to negatives before printing to increase their translucency.

The generic term for color print materials that make use of dyes incorporated directly into silver-gelatin emulsions in order to produce full color prints. These dyes combine with various chemical by-products produced during the development of exposed silver salts in the emulsion, which together form the coloring agents in the print. The completed chromogenic print consists solely of these synthesized dyes suspended in gelatin; all traces of silver are removed from the processing. Invented by Leopold Mannes and Leopold Godowsky, the process was acquired and perfected by Kodak and first marketed under the name of Kodachrome.

A dye destruction positive-to-positive photographic process used for the reproduction of film transparencies on photographic paper. The prints are made on a dimensionally stable polyester base as opposed to traditional paper base. Dyes embedded in the paper are bleached (destroyed) in processing. Because the dyes are fully formed in the paper prior to processing, they may be formulated with few constraints, compared with the complex dye couplers that must react in chromogenic processing. This has allowed the use of richly colored, highly stable dyes. It is a reversal process, meaning that it is used in printing transparencies

A photo-lithographic process that produces prints in ink from a photographic image made of gelatin. Like carbon (see above) and gum-bicromate (see below) printing, the collotype process is based on the light sensitivity of dicromated colloids. When ammonium or potassium dichromate is dissolved in gelatin and allowed to dry, the mixture becomes light sensitive. Areas absorbed to light lose their ability to absorb water and thus contact exposure under a positive transparency hardens the gelatin in proportion to the amount of light falling upon it. When an exposed plate is washed in water, blotted, and then rolled up with greasy ink, the plate takes up more ink where the exposure to light was greatest. This inked matrix is printed onto paper on a lithographic press. Under magnification, collotype images have a characteristic reticulated pattern from the gelatin surface.

The first successful collotypes were made by Alphonse Poitevin in 1855 using a lithographic stone coated with bicromated gelatin, a process he called "photolithographie". Various improvements quickly followed and by the 1870's there were a remarkable number of collotype processes, each with its own name: Albertype, atrotype, autogravure, autotype, heliotype, lichtdruck, photocollographie, photogelatin, phototypie, phototype, and phototint.

Usually a positive photographic print made by exposure to light through a negative placed in contact with light-sensitive paper. Contact exposure is necessary for those photographic papers that are not highly sensitive to light and therefore need exposure to the sun or another strong light source. Salted-paper prints, albumen prints, cyanotypes, gum prints, platinum prints, palladium prints, and the light-sensitive coating of heliogravure and photogravure processes all require contact exposures.

The process invented by Louis Jacques Mande Daguerre and published in September 1839. The process produced a unique camera image on a highly-polished, silvered copper plate. The silver of the plate was sensitized by the fumes of iodine to form silver iodide. After exposure in the camera, the latent image on the plate was made visible in the fumes of mercury and then fixed in sodium hyposulfite (now sodium thiosulfate). A whitish amalgam of silver and mercury formed where light had fallen. When the mirror-like surface of the daguerreotype reflected a dark background the image appeared as positive; when the plate reflected a bright background the image appeared as a weak negative.

Within a year or so of Daguerre's disclosure of his methods, several improvements by scientists and photographers were incorporated into the standard daguerreotype procedure. Several independent photographers added a brief fuming of bromine to the procedure to improve sensitivity of the plate and reduce harsh contrasts. In 1840, the French physicist Armand Hippolyte Louis Fizeau invented a means of intensifying or "invigorating" daguerreotype images by the use of sel d'or mixture, a mixture of gold chloride and ordinary photographic fixer. The chemical treatment (called "gilding") removed the surface fog, intensified the image and imparted a slight amber-rose hue to the plate. Manufacturers and photographers realized that since daguerreotypes were mostly viewed by lighting from the side a horizontal polishing and buffing of the plate improved image contrast.

Daguerre's original specifications required camera exposure from between three and thirty minutes making portraiture nearly impossible. Depending on lighting conditions, the character of the lens, and the nature of the sensitized silver surface, the improved daguerreotype procedures needed exposure times between four and sixty seconds. On average, studio portrait exposures were between ten to fifteen seconds.

Since the mercury-silver amalgam of the daguerroetype plate was extremely sensitive to abrasion, daguerreotypes were protected by metal mats and glass covers housed in frames or most commonly small decorative cases. The daguerreotype technique became obsolete by the end of the 1860's.

Direct Positive Prints On Paper (Bayard's Process)

A process invented by a French civil servant, Hippolyte Bayard, in 1839, that produced a unique positive image by exposure in the camera. The bleaching action caused by light striking silver chloride paper that had previously been darkened by exposure to sunlight and then sensitized with a weak solution of potassium iodide was the basis of the process. After an exposure that might run as long as an hour, the image was complete and the paper stabilized in a solution of potassium bromide or salt water, washed, and then dried.

It seems likely that Bayard invented the process after having first learned of the chemistry employed by Talbot for the preparation of photogenic drawing paper. The process, however, was not refined beyond its ability to supply unique positive prints.

A negative process employing an emulsion of gelatin and silver bromide. The emulsion is prepared by chemically forming silver bromide in the gelatin, "ripening" the mixture by heat to increase its sensitivity, and then removing the chemical by-products by washing. This emulsion is coated onto glass and then dried. After exposure, the dry plate is developed in an alkaline developer, not in an acidic one like those used for calotypes and wet-collodion negatives. This development (called "chemical" development) converts the silver bromide particles that have been altered by exposure to light (but not reduced to elemental silver) into silver particles.

The first successful (but crude) dry silver bromide images on glass were announced by the British photomicrographer Dr. Richard Leach Maddox in 1871. Previous experiments in making a dilver bromide-collodion emulsion in the mid-1860s reached a perfected stage in the late 1870s through the work of W.B. Bolton, but never achieved the sensitivity of wet-collodion plates. Although these dry collodion emulsion plates were convenient, they were less sensitive than wet-collodion plates, which also had to be prepared by the photographer. Reliable dry (gelatin) plates of a serviceable sensitivity were not available from manufacturers until 1878 when Wratten and Wainwright of London first successfully marketed their plates.

A generic name for the Polaroid Polacolor process. In this process the positive color image is transferred by the diffusion of dyes from a color negative to a paper support that holds the finished color print. After processing, the color print is separated from the negative, which is discarded. The first Polacolor materials were introduced in 1962.

A complex method for making color prints, in which a color transparency is photographed three times, using a different filter each time. The resulting black and white negatives contain all the necessary information for a full color image. The negatives are used to make three separate "matrixes", which are gelatin surfaces (on film) that absorb dyes in an aqueous solution in the three subtractive primary colors: yellow, magenta, and cyan. The dyes from these respective gelatin surfaces are transferred one at a time and in registration onto gelatin-coated paper. Although complicated, the technique allows for great control of hues and saturation. Dye transfer prints area among the most archivally stable of all color prints.

A process for toning photographic images containing silver that preserves them from chemical alteration by residual processing chemicals and atmospheric pollutants. (See albumen print and daguerreotype.)

A technique by which a layer of gum-bichromate is printed in registration over a preliminary image of platinum. See gum print and platinum print.

A positive printing technique employing a coating of pigmented, light-sensitive gum arabic that allows the photographer to manipulate the printed image during development. As with other colloids, such as gelatin, gum arabic (with watercolor pigment) is sensitized by the addition of ammonium or potassium dichromate to the mixture. This mixture is brushed onto paper by the photographer and dried. Contact exposure to a negative through strong light hardens the coating differentially according to the amount of light that passes through each part of the negative. During development in water insoluble or partially soluable areas may be lightened with a brush or other abrasive techniques. The first gum prints were exhibited in 1858 by the Englishman John Pouncy, but the technique did not become popular among photographers until the last decade of the century when it was brought to high perfection by the British photographer Alfred Maskell and the French photographers A. Roulle-Ladevaze and Robert Demachy. Edward Steichen and Alvin Langdon Coburn used the gum print to great effect, often coating preliminary prints of platinum or ferroprussiate (cyanotype) to make what were respectively called gum-platinum and gum-ferroprussiate prints.

A type of photogravure perfected in France in the 1840's and 1850's from the initial discoveries and observations of Joseph Nicephore Niepce that bitumen (asphalt) can be made light sensitive and used as a resist in etching a plate. In this process the resist is light sensitive as opposed to the common method perfected from Talbot's discoveries and experiments that used a layer of resist or a screen separate from the light sensitive coating. Charles Negre and Edouard Baldus each made important contributions toward the perfection of heliogravure in the 1850's.

A generic name for the Polaroid SX-70 process of color photography. In this process, synthesized color dyes migrate from the negative image to the surface of a sealed "film unit". The residual dyes in the negative together with by-products and reagents used for development are rendered harmless and invisible once processing is complete. The SX-70 process was introduced in 1972.

A color printing process in which sprayed dyes of the three subtractive primary colors (yellow, magenta, and cyan) and black are controlled by a computer from digitized information received from an optical scanning device.

A type of photographic printing paper coated with an orthochromatic emulsion which gives a high contrast print with very dense blacks when processed in Kodalith developer. It is a material normally used for graphic art work which, however, can be used to give a range of unusual effects if development is controlled. A brown or yellow appearance can result if a print is given less development time and over-exposed.

A positive printing technique identical to the platinum print except that the metal forming the image is palladium, which gives a palette of brown and sepia hues. See platinum print.

Any assembly of separate photographic images brought together to form another picture by collage.

The first name given by William Henry Fox Talbot to the photographic process that he announced in January 1839. "Superfine writing paper" was dipped in a weak bath of common salt and after blotting was brushed with a solution of silver nitrate. The light-sensitive silver chloride formed in the fibers of the paper was not highly sensitive to light and after the photogenic drawing paper was prepared and dried it required exposure in direct sunlight from ten minutes to an hour depending on what object (leaves or lace) or image (waxed engraving) had been placed over it. Talbot fixed the resulting image, which had printed-out during exposure, in a moderately strong solution of potassium-iodide or a strong solution of common salt. We now consider these prints to be "stabilized" rather than fixed. Treatment with potassium iodide created a very pale primrose yellow hue in the highlights while common salt produced a pale lilac tint.

Photogenic drawing paper intended for camera exposures had to be more sensitive, and thus Talbot coated the paper as many times as he could, alternating between common salt and silver nitrate, before the paper would spontaneously blacken on its own. With an f/11 lens, these exposures ranged between one and two hours. The negative camera images were formed by printing-out and not by development, which was a later discovery (see calotype). As early as February, 1835, Talbot had printed photogenic drawing negatives as positives (which he then called "transfers"). In order to successfully print the weak images of camera negatives, Talbot devised a negative paper in February/March 1839 that was based on silver bromide, and which was more responsive to light than even the multiply coated silver chloride paper. These new negatives of considerably higher contrast produced better positives on the original photogenic drawing paper. When the calotype process became the standard way of making camera exposures, Talbot printed these negatives on photogenic drawing paper, as well.

A photograph made (without a camera) usually by laying objects directly on the light-sensitive surface. Images obtained in this way are negative silhouettes and transcriptions of the translucent areas of the objects. In the 1920's the technique was used by Man Ray (developed photograms) as a dada expression and by Laszlo Moholy-Nagy (both printed-out and developed photograms) as a constructivist technique.

A method by which a photographic image formed in bichromated gelatin is used to control the etching of a metal plate for printing in ink. In the early 1840's, several experimenters tried to etch daguerreotypes, but with limited success. In the 1850's, Talbot discovered a method of photographically controlling the rate at which the acid would etch the metal plate. Talbot coated his metal plates with gelatin mixed with potassium dichromate, dried the coating, exposed under a positive transparency (made from the original negative), developed in water and then etched the plate. In order to provide a rough surface to hold the ink on the plate, he dusted the coated plate with acid-resistant resin or imposed a lined screen (from gauze) on the image. After later perfection by the Czech Karl Klic in 1879, the "Talbot-Klic" method became standard for the production of photogravure. Klic first dusted the plate to be etched with acid-resistant resin and then transferred a carbon print onto the plate. Iron chloride etched the plate to different depths in proportion to the tone in the picture (in reverse proportion to the thickness of the carbon tissue). The plate was inked by hand and printed in an etching press. Photogravure was a favorite printing technique of Peter Henry Emerson and Alfred Stieglitz, as was popular from the 1880's through the early 1920's. Later, etched cylinders that were mechanically screened and inked formed the basis of a process still in use, rotogravure, which prints plates at relatively high speeds.

Another technique for obtaining photographic etched plates, called heliogravure, was perfected in France. See heliogravure.

A method of making a single photographic print by the superimposition of various negatives or copying a photocollage.

Pigment prints are made by digital inkjet printers, which mix ink to create specific hues. The ink is then applied directly to paper in fine detail, measured in DPI (dots-per-inch).  Photographic prints made on inkjet printers that use pigment-based inks are commonly referred to as archival pigment prints which contain a more stable dye.  

A positive printing technique that employs light-sensitive iron salts to form a provisional image that is subsequently made visible by conversion into platinum metal. The process was invented and patented by the Englishman Richard Willis in 1873. Papers supplied by the Willis Platinotype Company of London and other manufacturers contained an iron salt (probably ferric oxalate) and platinous potassium chloride. After contact exposure through a negative, the paper was developed in potassium oxalate. The dilution of the exposed iron caused the platinum salt to be reduced to pure, elemental platinum. The print was immersed in a very weak bath of hydrochloric acid, washed and dried. Depending on the constituents of the sensitizer or developer, platinum prints range from neutral black to warm rose-sepia hues.

Platinum paper was many times more permanent than photographs that used silver to form the image. It also was favored by photographers for its broad range of subtle gray tones and its lack of coating on the paper. After the 1920's, platinum papers were difficult to obtain outside of England, where after 1936 they were discontinued.

A generic name for a photographic paper which does not need to be developed in order to make its image visible. The printed-out image darkens by itself during exposure to light. As the image darkens, it also shields the remaining light-sensitive chemicals underneath, and thus provides a control for exposure and an adjustment to negatives of high contrast. Printing-out papers are known for the broad, delicate tonal range.

The name given by Man Ray to his photograms. See photogram.

A positive print made without an emulsion or thick coating, in which the light-sensitive silver salts are soaked into the paper. Talbot preferred silver chloride, but silver iodide, silver bromide, and silver oxalate were also used in combination. Sometimes the addition of starch (arrowroot) improved the color, as well as the strength of the image by preventing the silver salts from penetrating too deeply into the paper. These papers were prepared with non-light-sensitive salts and sensitized with silver nitrate shortly before use. Salted-paper prints have finely divided silver particles on their surface that are sensitive to atmospheric pollutants and humidity, and thus fade easily. See photogenic drawing.

A brand name for a short-lived photogenic paper marketed by the Willis Platinotype Company based on the chemistry of platinum paper, in which the final image was formed by a mixture of silver and platinum. Satista paper was produced during World War I when platinum was needed in various war industries.

The generic name for the common black and white photograph employing an emulsion of light-sensitive silver salts (usually silver bromide) ripened in gelatin to form an emulsion. See description of emulsion under dry plates.

A generic name for the instant black and white developing process devised by Edwin H. Land and first introduced in 1948 through the Polaroid Corporation. This process relies on the light sensitivity of silver halides, which after exposure in the camera are developed within a specially designed film/print sandwich (film unit) to form a negative silver image. The underexposed silver halide unaffected by development is made soluble by a special reagent and in this state migrates from its original support, through the reagent, to a new support where it is reduced to silver and forms a positive image. In Polaroid film type 55 both a film negative and a paper positive are produced. The type 55 negative can be used to make positives by conventional methods.

A term used to describe the phenomenon of the partial reversal of tones in a developing photographic emulsion or material after an additional exposure to light. The phenomenon is more accurately referred to as the "Sabattier effect" after the Frenchman who first observed in 1860. This technique was accidentally discovered by Lee Miller and Man Ray in 1929.

A card mount holding a pair of stereo images. The phenomenon of stereoscopic vision was discovered by the Scottish scientist Sir David Brewster in 1837. Photography proved to be a better medium for representing scenes stereoptically than drawing because of the ease in which it recorded the difference between the two points of view that each eye perceived.

A negative process invented by the British photographer Frederic Scott Archer in 1851 that used collodion (a mixture of nitrocellulose dissolved in ethyl ether and ethyl alcohol) as a vehicle to hold light-sensitive silver iodide on a glass plate. Because collodion dries to be water-proof, it had to remain moist during exposure and up to the time of development. Thus, all wet-collodion plates had to be prepared in the darkroom immediately before exposure and developed immediately after. This meant that the photographer in the field had to have a portable darkroom nearby. The inconvenience of this procedure was offset by the relatively fast speed of the coating and the sharp images that could be printed from it due to the glass support. Although plagued with many problems, the wet-collodion process was the standard negative process from the mid-1850's through the 1870's.

In the process that came to be modified by photographers several years after Archer's publication, a mixture of ammonium or potassium and collodion was poured onto a glass plate, the coated plate was immersed in a bath of acidified silver nitrate for about three minutes and then withdrawn and exposed in the camera. After exposure, the plate was developed in pyrogallic acid or ferrous sulfate, rinsed in water and fixed in ordinary hypo. At times photographers used the potentially lethal potassium cyanide as a fixer because it produced negatives with absolutely transparent shadows by removing the overall fog that typically covered collodion negatives after development. After fixing, the plate was washed, dried, and then varnished to protect the fragile and easily abraded negative image.

By using the ferrous sulfate developer, the wet-collodion process was easily adapted to the production of direct positives on glass (ambrotypes) or on blackened metal (tintypes). See ambrotypes.

The present glossary is based on one published by David Travis for a exhibition on the history of photography for the National Museum of Art, Osaka, in 1984, to which lengthy passages have been added from a detailed study of the history and development of nineteenth-century techniques prepared by Joel Snyder.