Photographs

Identification of historic photographs

The wide range of materials used in producing photographic images has led to a wide range of deterioration patterns. This means that some historic photographs need to be treated differently to others. For example, it is recommended that original albumen prints are not exhibited at all—copies should be made for exhibition. Carbon prints, however, can be exhibited safely if standard exhibition precautions are taken.

Correctly identifying the process is important. In many cases the deterioration pattern can help identify the process used.

Daguerreotype: 1839–c1860

Structure. The daguerreotype consists of a positive image formed by mercury vapour on a highly polished coating of silver on a copper plate. It is usually in its own decorative and protective case.

The Daguerreotype is in the centre of the bottom row. On either side of it and above it are the components of the case. Photograph courtesy of Artlab Australia, reproduced with permission of the Art Gallery of South Australia

Appearance of image. The daguerreotype has a silver, mirrored surface. The image changes from positive to negative depending on the viewing angle. This is the main key to identification.

Deterioration. Tarnishing is the most common problem and can cover the entire surface of the plate. Copper corrosion can occur, where the fractured silver layer exposes the underlying copper layer, leaving behind green and blue copper salts. Black spots and accretions are sometimes found over the plate. Evenly distributed spots may be the result of residues from the original processing. Another potential problem is the large needle-shaped silver sulphide crystals which are formed within deeply tarnished films. Flaking, usually around the edges, is often the result of excessive gold toning.

Ambrotypes: 1851–c1880s

The ambrotype is a variant of the wet collodion process.

A cased ambrotype. Photograph courtesy of Artlab Australia, reproduced with permission of the Art Gallery of South Australia

Structure. The ambrotype is an under-exposed collodion emulsion on glass. It appears as a negative until a black backing turns the image into a positive.

Ambrotypes usually have their own decorative and protective cases.

Appearance of image. The ambrotype has quite low contrast—the whites appear as dull grey and detail is less visible in the shadow areas. It can be viewed from all angles.

Deterioration. The collodion emulsion may weaken, crack or flake. It may also separate from the glass.

Decomposing collodion releases gases, such as nitric oxide and nitrogen oxide, which combine with atmospheric moisture to form nitric acid—this attacks the cellulose in the collodion.

Atmospheric pollutants and residual processing chemicals can cause the collodion image to deteriorate.

Silver sulphiding will appear as red and green discolouration.

The glass support can break and glass splinters can scratch the emulsion.

If the ambrotype is varnished, UV radiation may cause discolouration and yellowing of the varnish.

The painted black backing often flakes off, leaving what appear to be holes in the image.

This ambrotype had a flaking black backing. This photograph was taken during conservation treatment. The photograph is intact—the area on the right has had the black backing removed. After the flaking backing has been fully removed, it will be replaced with black cardboard and the image will be clearly visible. Photograph courtesy of Artlab Australia, reproduced with permission of the Art Gallery of South Australia

Tintype, ferrotype, melainotype: 1854–c1930s

A mounted tintype. Photograph courtesy of Fred Francisco

Structure. The tintype was a variation on the ambrotype and was a method for making direct, positive images in the camera on a black or chocolate-brown, enamelled iron plate.

The plates were originally coated by the wet collodion process; but dry plates were later manufactured.

Unmounted tintypes are easily identified by their iron base.

Appearance of image. Tintypes have little contrast. Whites appear as dull grey and shadow areas have little detail.

Deterioration. The collodion emulsion may become weak, crack or flake. It may also separate from the plate.

Decomposing collodion releases gases, such as nitric oxide and nitrogen oxide, which combine with atmospheric moisture forming nitric acid-this attacks the cellulose in the collodion.

Atmospheric pollutants and residual processing chemicals can cause the collodion image to deteriorate.

The iron support may bend or be deformed, cracking the collodion emulsion. This often occurred because many tintypes were sent through the mail.

Thin lines of rust can be seen under raking light on some tintypes.

Opaltypes: c1890s

The opaltype is a photographic image on opaque white glass.

Opaltype with overpainting. Photograph courtesy of Fred Francisco

Structure. The photographic image is on an opaque white glass.

The base image is usually black and white, but often heavily overpainted.

Overpaint is smudged when attempts are made to dust or clean the image.

Deterioration. The glass support often breaks, and there can be subsequent loss of image from chipping along the break.

Overpaint is smudged when attempts are made to dust or clean the image.

The overpaint can become quite dirty and/or stained.

IMPORTANT: The overpaint is usually very soluble in water—don't attempt to clean the surface.

Salted paper prints: developed 1839, widely used 1860–c1890

Structure. One-layer structure—the visible image is formed directly in the paper. The light-sensitive material is embedded in the paper.

Appearance of image. The image is reddish-brown, purple or yellow-brown when processed properly; it can be lilac, pale-blue or a lemon yellow if improperly processed.

The paper fibres are clearly visible under magnification.

Deterioration. The paper used in salted paper prints is susceptible to the same sorts of deterioration as other papers—it becomes brittle, stained and acid burnt.

The prints fade quickly because of improper processing, atmospheric pollution, poor-quality adhesives and mounting materials, resulting in:

• variations in colour;

• edge fading; and

• small yellow dots and lack of highlight detail.

Exposure to UV radiation for prolonged periods causes severe fading.

Platinotypes: 1880–c1930

Structure. Platinotypes have a one-layer structure.

Appearance of image. Platinotypes have a very stable image: there is no fading or silvering out. They are silvery-grey in colour, with a matt surface.

The paper fibres are clearly visible under magnification, and give a rich, velvety texture.

Deterioration. The image, itself, is stable with no fading or silvering out. The processing includes acidic cleaning baths, which contribute to the deterioration of the paper.

Platinum prints are brittle, often with cracked or broken corners.

Residual iron salts plus the acids which are present, contribute to the eventual discolouration of the paper.

Cyanotypes: used c1885–c1910, very rare 1842–1880

Structure. Cyanotypes have a one-layer structure.

Appearance of image. Cyanotypes have a uniform, bright blue image. The surface is matt, with the paper fibres clearly visible under magnification.

Deterioration. The paper used in cyanotypes is susceptible to the same sorts of deterioration as other papers—it becomes brittle, stained and acid burnt.

A cyanotype showing the characteristic, blue image colour. Photograph courtesy of Fred Francisco

The blue image fades but can be partially restored by storing it in the dark.

IMPORTANT: Alkaline conditions will fade the blue image; therefore alkaline-buffered enclosures should not be used with cyanotypes.

Albumen printing-out papers—POP: 1850–c1890

Structure. An albumen print is a two-layer system, with an albumen layer holding the sensitised silver on top of a paper support.

Appearance of image. Albumen prints generally produce detailed images.

An albumen print with characteristic fading of the image. Photograph courtesy of Fred Francisco

It is possible to see the paper fibres through the binder layer in highlight areas, when examined under magnification.

Albumen prints can be warm red-brown, a yellow-brown, purplish-brown or purplish-black. Most albumen prints are yellow in the highlight areas.

Deterioration. Typical damage includes fading, yellowing of highlight areas, brittle paper and cracking of the albumen.

Oxidative-reductive deterioration of gold-toned, photolytic silver images results in loss of detail in highlight areas, overall fading of the image and a change in image colour from purplish-brown to warmer, yellower hues.

Sulphiding deterioration, resulting from thiosulphate retained after insufficient washing or from contamination by sulphur in atmospheric pollutants, causes the image to fade to a yellow-brown or to a greenish colour. In some cases, the retention of silver thiosulphate due to the use of exhausted fixer baths, results in the image fading to a greenish-black colour. There is much more staining, usually greenish-yellow, in non-image areas.

Tinting dyes, added to albumen to counteract the warm tones of the image, are extremely unstable and fade readily. High temperatures and relative humidity will also adversely affect these dyes.

Structural problems lead to severe cracking of the albumen layer.

Yellowing of the albumen layer is caused by a protein-sugar reaction. Storage and display conditions are critical in controlling the rate of this reaction, and therefore the extent of yellowing. The key environmental factors are relative humidity, and exposure to UV radiation and to visible light.

Gilt inks were often used in association with albumen prints on cartes-de-visite. These inks, made with bronze powder and zinc, flake quite readily. When the flakes come into contact with the image, they cause local discolouration and spotting of the photographic image.

Albumen prints have a strong tendency to curl when they are not stuck down to a backing.

Collodion printing-out papers—POP: 1880–c1910

Structure. Collodion papers are a three-layer system with the paper support, a baryta layer over the paper—completely hiding the paper fibres—and the collodion emulsion layer on top of the baryta layer.

Appearance of image. The colour of a collodion print varies, depending on the halide salts and toners used during processing.

Glossy collodion prints were usually gold-toned and had a warm tone.

Matt collodion prints were usually gold and platinum-toned and had an olive-black tone. Matt prints were also more stable and resisted fading.

Pigments or dyes were sometimes added to the baryta layer of collodion papers, to make them appear reddish or bluish in colour.

Deterioration. The collodion layer is not flexible. Movement in the paper support due to changes in relative humidity causes hairline cracks to appear in the surface. But, unlike albumen prints, these hairline cracks do not become larger.

Poor storage and handling are serious problems, because the emulsion layer is extremely thin and has very poor resistance to abrasion.

For glossy, gold-toned prints, oxidative-reductive deterioration includes loss of highlight detail, a shift in image colour from purple to warm, reddish-brown and overall fading. Image deterioration is often accompanied by silver mirroring—silvering out—and abrasive damage.

Matt prints are much more stable and show less fading, mirroring and colour change.

Sulphiding deterioration includes fading of the highlights and an intermediate stage of blackening of the image in the middle tones and shadows, followed by fading of the image to a yellowish or greenish-brown.

Matt collodion prints are less affected by sulphiding than glossy collodion prints.

Gelatine developing-out papers-DOP: 1880–present

Structure. Gelatine prints have a three-layer system, with the paper support, a baryta layer over the paper—completely hiding the paper fibres—and the gelatine emulsion layer on top of the baryta layer.

Appearance of image. The paper fibres are not visible through the binder layer.

Gelatine developing-out papers have a near-neutral image colour: a soft slate-grey which sometimes has a greenish-grey caste.

Silver gelatine print—a chemically developed image. Photograph courtesy Artlab Australia, reproduced with permission of G.M. Thompson

Print surface may be glossy or matt.

Deterioration. The most common types of image deterioration are caused by oxidative-reductive reactions, resulting in:

• overall fading;

• loss of highlight detail;

• yellowing in the lighter areas of the image, fading of lighter tones and overall fading; and

• silver mirroring—silvering out—in shadow areas. Nearly all 19th century gelatine developing-out prints are affected.

In advanced cases of oxidative-reductive deterioration, the original black image colour fades to yellow-brown with yellow highlights. These colour changes are caused by physical changes in the filamentary silver on a sub-microscopic level.

Sulphiding: the symptoms of sulphiding resemble those of oxidative-reductive deterioration.

A silver gelatine print showing overall fading of image. Photograph courtesy Artlab Australia, reproduced with permission of B. Pring

Silver gelatine print with silver mirroring—silvering out—around the edges of the photograph. Photograph courtesy of Artlab, reproduced with the permission of Ann V. Nicholas

If you have a problem related to the identification, treatment, storage or display of photographs contact a conservator. Conservators can offer advice and practical solutions.