Structure of a photograph
- Primary support: metal, glass, paper, plastic material
- Image layer: binder (albumen, collodion, gelatine) + image material (usually silver compounds)
- Barite layer (barium sulphate): present in materials since 1880 with the function of separating the image layer from the paper fibres
- In some photographs, there is a secondary support: cases, frames, mounts, albums.
Definitions of printing techniques
Procedure for 1-layer image
The image is formed directly on uncoated paper.
Procedure for 2-layer image
The image is formed with a binder layer on which there are light-sensitive compounds.
Procedure for 3-layer image
The image is formed with a binder layer which in turn lies on a layer of barite that completely separates the image from the paper.
Printing-out
A procedure by which the image is formed solely through exposure to the sun. The photographic plates are then immersed in a solution that blackens the emulsion in the points just affected by the filtered light from the lens and corresponding to the illuminated parts of the external image. Used for contact printing with salted, albuminata, cyanotype, and aristotype papers.
Development
This phase of the photographic process consists of a bath which makes it possible to make the latent image visible by reducing the silver halide grains to metallic silver by exposing them to light.
Photographic processes found in the photographic collections of Phaidra
Albumin
- Photo print by printing-out process
- Structure of the photograph: 2-layer image
- Primary support: paper
- Binder: albumen
- Image: silver compound
- Secondary support: mount, frame, album. The image can be separated.
- Date: 1855-1900 and beyond
Image taken from Studies of ethnology of India in Phaidra
Definition
Mainly used for the preparation of photographic negatives on glass plates. The process, credited to Abel Niépce de Saint-Victor in 1848, has characteristics based on some properties of albumen, a major protein constituent substance of cells and other plant tissues. It is extracted from egg white for use in photography. It was first used as a means for maintaining the silver salts in the manufacture of negatives on glass plates and then in the manufacture of albuminata paper, according to the technique invented by Louis Desiré Blanquart-Evrard in 1850. The paper was covered with egg white in which potassium bromide and acetic acid had been dissolved. Once dry, the paper would be slightly agitated on the surface by a silver nitrate solution, then again dried. The coated paper was placed in contact with the negative in a glass frame, and exposed to sunlight for several minutes, sometimes for hours, until an image appeared. Then the print was placed in a gold chloride solution that gave a tinge of intense brown, fixed in sodium hyposulphite, thoroughly washed and dried.
Identification
Video
Albumen: history, science and conservation
Aristotype (or collodion or gelatine to printing-out)
- Photo print by printing-out process
- Structure of photograph: 3-layer image
- Primary support: paper
- Binder: collodion or gelatine
- Barite layer
- Image: silver compound
- Secondary support: mount, frame, album. The image can be separated.
- Date: 1860-1916 circa
Elis. Bommer in the Botanists Portrait Collection in Phaidra
Definition
The method invented by Liesegang around 1886 includes the positive collodion printing-out and positive gelatine printing-out (silver-citrate paper). The aristotype paper was ready-to-use, that is, printable upon exposure to direct sunlight that, thanks to the gold chloride, acquired intense shades of brown and then had to be immersed in a fixing bath to attach particular colours to the printed copy. The aristotype papers had a remarkable diffusion, almost completely replacing albuminate papers, but around 1920, they in turn fell into disuse.
Identification of collodion POP prints
Identification of gelatine POP prints
Salted paper
- Photo print with printing-out process
- Structure of photograph: 1-layer image
- Primary support: paper
- Image: silver compound
- Secondary support: mounts, frames, albums. The image can be separated.
- Date: 1839-1850/60
Asa Gray in the Botanists Portrait Collection in Phaidra
Definition
Invented by William Henry Fox Talbot in 1840, it was adopted by Louis-Désiré Blanquart-Evrard who, in 1846, experienced with a more rapid method of printing. Sheets of drawing paper soaked with sodium chloride were covered – on a single surface – in a silver nitrate solution. The surface coated with nitrate was then placed in contact with a negative and, exposed to light, the silver salts were transformed into metallic silver, leaving a reddish effect on the image. After printing-out, it was turn and fixed. Used mainly for the production of photogenic images and calotypes.
Cyanotype (or iron salt print)
- Structure of the photograph: 1-layer image
- Primary support: paper
- Image: iron compounds
- Secondary support: box, mount, frame, album. The image can be separated.
- Date: 1839-1920 circa
Imagine from The Botanic Garden of Padua in 1895 in Phaidra
Definition
Printing on cyanotype paper. Photographic reproduction by direct contact was developed by Hershel around 1842, non-silver complex, but based on the sensitivity of ferric salts. Also called procedimento al ferroprussiato.
Daguerreotype
- Unique: positive/negative image
- Primary support: silvered copper plate
- Image: silver and mercury
- Secondary support: box, frame
- Date: circa 1839-1855/60
Two stereoscopic daguerreotypes in the collection Pre-cinematic tools of the Museum of the History of Physics in Phaidra
Definition
Unique photochemical image on a copper plate or direct positive with left and right inverted with respect to the subject. In 1839, Louis Jacques Mandé Daguerre had discovered the latent image on the silver-coated copper plates (16x21 cm), which appeared with mercury vapour. To obtain a daguerreotype the procedure was generally as follows: (1) Cleaning and polishing a silvered copper plate; (2) Coating of the plate by means of the iodine vapour: this operation was made inside a special box and served to form a thin layer of silver iodide on the surface of the plate itself; (3) Processing by means of heated mercury vapour which, once deposited on the parts exposed to light, turned clear in the dark field; (4) Fixing with sodium hyposulphite. The plates used were standardised measures: 21.5x16.5; 10.5x8; 7x5.5; 16x12; 8x7 cm.
Negative on gelatine plate
- Primary Support: glass
- Image: silver compound
- Date: 1871-today
Gaspard Bauhin in the Botanists Portrait Collection in Phaidra
Definition
In 1871, Richard Leach Maddox invented a method to dissolve gelatine in water by adding a cadmium bromide solution and then silver nitrate. These products reacted to form silver bromide crystals suspended in gelatine. The emulsion was spread on the plate and allowed to dry. Richard Kennet in 1873 devised a practical method to filter the emulsion.
Platinotype
- Structure of photograph: 1-layer image
- Primary support: paper
- Image: platinum
- Secondary support: mount, frame, album. The image can be separated.
- Date: circa 1873-1920
William Berryman Scott in the Geologists Portrait Collection in Phaidra
Definition
Palladium paper printing with platinum salts, credited to William Willis between 1873 and 1879, is based on the properties of iron salts passing from the ferric state to the ferrous state upon exposure to light. In the presence of formation of ferrous salts, platinum salts, if developed in potassium oxalate, are transformed into platinum, far more stable than silver. The coated paper was put on the market by Platinotype Company of London.
Gelatin print processing
- Photo printing development
- Structure of photograph: 3-layer image
- Primary support: paper
- Barite layer
- Image: silver compound
- Secondary support: mount, frame, album. The image can be separated.
- Date: 1874-today
Borgomagno (Padova). Locomotiv after an aerial machine-gun fire in the CASREC Photo Archive in Phaidra
Definition
Gelatine paper
Paper, well-coated, covered by a uniform layer of gelatine, which still represents the base for various types of photographic prints.
Gelatin paper – silver bromide
Gelatin paper coated with a silver bromide emulsion. Invented by Joseph Maria Eder in 1884.
Gelatin paper – silver chlorine-bromide
Gelatin paper coated with silver chlorine-bromide.
Gelatin paper – silver chloride
Chloride paper for contact printing, produced around 1890 on an idea by Joseph Maria Eder (c. 1884), regarding gelatine coated with an emulsion of silver chloride. Less sensitive than silver bromide, also known as Gaslight paper.
Definitions on this page are from the AIB. Glossary of photographic terminology by Laura Corti and Fiorella Gioffredi Superbi.