Glossary

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.
 

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 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.
 

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.
 

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.
 

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.
 

Another name for blueprint. The cyanotype or ferroprussiate process was invented in 1842 by the British astronomer and chemist Sir John Herschel. It is based on the light sensitivity of various salts of iron. Typically ferric ammonium citrate and potassium ferricyanide are mixed in an aqueous solution and applied to paper. When dry, the paper is exposed by contact to sunlight until a deep, olive gray image appears. The print is then placed in water which changes it to a rich blue. If continuous-tone prints are desired, potassium dichromate is added to adjust the contrast of the print to the character of the negative.
 

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.
 

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 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 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 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 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. Palladium gives a palette of brown and 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.
 

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 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 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.