Care and Identification of 19th Century Photographs
  • Chapter 1)
    • Photogenic drawings, though very rare, are the ultimate ancestors and archetypes for all of the silver printing out papers used during the 19th century.
    • Printing out papers – sensitized paper where the image appears spontaneously during exposure
    • Developing out papers – chemical treatment is required to make the image appear
  • 2) Component materials of prints and deterioration
    • Components of a photo
  1. Final image material
  2. Binder
  3. Support
  4. Secondary support
  5. Surface treatments/adhesives
    • The most important final image material in 19th century photos is metallic silver
    • Deterioration for silver images
      • The two basic mechanisms by which silver images deteriorate are sulfide and oxidative-reductive deterioration
        • Sulfiding – silver is reacting with sulfur to create silver sulfide – silver tarnish. Usually the sulfur comes from with in the photo through residual processing chemicals. You can wash the photo in water to get the chemicals out but it can be difficult in paper, gelatin and collodion prints.
        • Symptoms – the image turns yellow in highlights and begins to fade
        • Oxidative-Reduction deterioration – oxidants convert silver atoms into silver ions and ultimately back into silver. It causes fading, mirroring and shifts in image hue (to reds and yellows) – moisture plays a central role in oxidation
    • Environment – RH should be 30-40%. While temperature is important because higher temperature speeds up chemical reactions, RH is key for photo longevity
    • Deterioration of different photo types
      • Toned prints – gold and platinum are much more stable and resistant to sulfiding and oxidization
      • Platinum prints are very stable however they can transfer their image or degrade paper so they should be sleeved or at least interleaved in storage
      • Cyanotypes – subject to fading, also you should not treat them with alkaline solutions or store them in alkaline buffered paper enclosures
      • Pigment and dyed photos are very light sensitive
      • Binders and their deterioration
      • Albumen – egg white, tends to yellow over time. RH affects the yellowing and also exposure to light and acidic papers (mounting boards). When albumen prints start sulfiding (from improper washing) it creates an unfixable silver protein compound and yellow effect. Albumen is the only binder that has this problem. Albumen will become brittle and crack or soften and swell in RH swings.
      • Gelatin – will swell and contract or turn brittle in different RH and at 80 degrees Fahrenheit it will turn into a liquid. When it is stored in plastic sleeves in high RH it will stick to the plastic (called ferrotyping) and high RH will speed up the oxidization
      • Collodion – will exhibit small cracks. It will not yellow like albumen but it can dissolve in many solvents
    • Photo supports
      • Paper Supports - photograph papers had to be made of such good quality to withstand the chemicals used, that photo paper is one of the most stable paper objects in existence.
      • Secondary supports – when the paper was thin it had to be mounted on a secondary support (albumen prints) to resist curling, most often the secondary support is an acidic mat board
    • Brittle mounts should be supported on acid free board. Also keep acidic mounts from touching other photos, so interleave them in storage
    • Unmounted albumen prints will curl very tightly albumen side in. The must be put in a mat or some other rigid support and the RH managed to prevent curling which will cause the albumen to crack.
  • 3) Stability of specific print media
    • Foxing – caused by mold growth or iron or copper impurities in the paper. RH directly affects foxing and high RH speeds it up
  • 4) Identification of photograph and photomechanical print processes
    • Photographic print – a piece of paper that at one time was sensitive to light
    • Photomechanical print – may bear a photographic image, but was never light sensitive (was made by a printing press)
    • The basic tools for identification of photo are:
  1. Hand held magnifier
  2. Low power stereomicroscope
    • Daguerreotypes – a positive image on a thin copper plate with a mirror like coating of silver. It can appear as a positive or negative depending on the angle of view and usually displayed in cases.
    • Ambrotype and tintype – both are a positive physically developed silver image in a collodion binder on an opaque non-reflective support. In reflected light these images have a characteristic creamy, whitish appearance because of the size of the silver particles.
    • Ambrotype – a photo on a glass support with a black background and stored in a case. The image only appears as a positive when viewed against the black background. Inside its case it will appear positive no matter what angle you view it.
    • Tintype – Support is made of a thin sheet of lacquered iron, easy to identify because of the support. If it is in a case it can be hard to identify, but you can put a small fairly strong magnet against the glass and it should stick to a tintype and not ambrotype.
  • Identification guide

Steps to identifying prints

  1. grain pattern
  2. determine the layer structure
  3. individual characteristics
    • Photomechanical prints may stain but do not fade.
    • Photomechanical grain patters (under 30X)
  1. Letterpress – half tone – sharp edged regular dots
  2. Photogravures – fine detail, variable ink deposit, aquatint grain (fine irregular pattern) and the paper usually has an embossed plate mark
  3. Callotypes – fine detail, reticulated grain pattern (looks like a mosaic) no plate marks
  • Photographic print types
  1. Single layer – print is directly on the paper – the paper grain is visible and the image has a matte surface
  2. Two layer – paper support and a binder – a coating of transparent material that contains the image (usually glossy or has some kind of sheen)
  3. Three layers – paper, baryta layer and binder – baryta is a coating of white pigmented gelatin which covers the paper support forming a smooth deflective substrate for the binding layer – examine the highlights under a microscope – the paper fibers will not be visible because of the baryta layer.
    • Single layer prints – (paper fibers are clearly visible)
  1. salted paper prints – the image is a reddish-brown, purple or yellow-brown and generally show signs of image fading
  2. cyanotype – bright uniform blue print
  3. platinotype – neutral black or warm brownish-black with no image fading. Platinotype specific deterioration – catalytic transfer image and deterioration in the primary support paper
    • Two layer prints
  1. Albumen print – localized or overall image fading. Unfaded images are purplish-brown or purple and usually have good highlight detail. Signs of fading are a yellowish-red color, overall lightness and loss of highlight, yellow spots, fading at edges, blotchiness and silver mirroring. The surface is smooth with no relief and many prints show a crackling of the albumen layer and the albumen is generally yellowed
  2. Carbon print – (use pigments so can be in any color and do not fade). There is an image relief effect – the gelatin layer is thick in dark areas (no paper fibers are visible) and thin in light areas. They can show mosaic light crackles, usually in the dark areas of the print and under 30x magnification will show flecks of undispersed pigment.
  3. Woodbury types - (use pigments so can be in any color and do not fade). Woodbury and carbon prints are virtually identical and display the same characteristics. Carbon prints are photographic prints while woodbury types are photomechanical. Woodburys have a more prominent image relief, they are small, never larger than 11 X 14, and generally are used as book illustrations and are labeled
    • Three layer photos – have warm image hues and use gelatin or collodion printing out paper
  1. Matte collodion printing out papers toned with gold or platinum – thin baryta layer so some paper fibers are visible – little to no fading or silver mirroring. They may have a little yellowing and have excellent preservation, but are prone to surface abrasion
  2. Gelatin printing out papers – dominant paper from 1905 to 1960 – shows near neutral black image color, has a relatively thick baryta coating and frequent presence of silver mirroring.
  • 5) Preservation and collection management
    • The essential goal in managing a photograph collection must always be to use photos in ways that do not contribute to their destruction
  • 6) Storage
    • RH is the single most important environmental agent and the key to preservation or destruction of 19th century photos
    • 0-30% (low RH) – all chemical deterioration processes that require water (oxidation) are either completely stopped or slowed to a minimum and mold growth is virtually eliminated. Unsuitable for storage because it makes paper, albumen and gelatin so brittle it can be damaged with handling and causes shrinkage
    • 30-50% (moderate RH) – perfect for storage – dry enough to inhibit chemical or biological deterioration and most enough to keep celluosic materials and proteins flexible, prefer 30-40% (lower than typical storage for paper to inhibit oxidation) this environment is not appropriate for all materials
    • 50-100% (high RH) – the higher the RH the more the damage increase: oxidation sets in at 60% and fungus and molt at 65-70%
    • Even at room temperature serious fading occurs within days when albumen prints are exposed to high humidities.
    • Albumen yellows faster at high RH – the lignin breaks down faster and the acids migrate faster causing deterioration of the paper and woodburn.
    • Mold growth starts at 65% and photos are the perfect food for it.
    • RH fluctuation causes – binder cracking, delamination, tears and irreversible warping
  • Controlling the environment
    • A rise in temperature will lower RH and cooling the air will drive RH up inside a building
    • When temperature humidification is needed the best method is an unheated evaporative humidifier, but be sure the unit is kept clean.
    • Heat is a form of energy that increases the rate of nearly all chemical reactions, including those that cause deterioration.
    • Daily fluctuations of 7 degrees should be avoided.
    • Two important oxidant gasses are: nitrogen dioxide and ozone.
    • Effects of oxidant gasses on photos
  1. Fading
  2. Discolored and embrittled paper
  3. Weakened binder layers
    • Three tier approach to protect your collection vs. oxidant gasses
  1. Air purification
  2. Find and remove local sources of oxidant pollution
  3. RH control
    • Potential sources of oxidant gasses
  1. Fumes from curing oil-based paints
  2. Electrostatic copiers
  3. Wood and wood finishes
  4. Cosmetics and cleaning supplies
    • Hydrogen sulfide gas tarnishes silver
    • The ideal storage environment controls temperature, RH and has air filtration and purification machines.
    • Where environmental conditions are less than optimal, the quality of storage materials become much more significant, enclosures should be archival and conform to ANSI and PAT standards and testing.
    • Alpha-celluose papers are more permanent
    • Be careful of buffered papers. Buffered papers are good for B&W photos but not cyanotypes and buffering can yellow albumen prints.
    • A general principal in boxing prints is to match the sizes of prints and their enclosures as closely as possible to the dimension of the box so as to minimize damage from the shifting of the prints.
  • 7) Handling, display and care
    • Prints have almost no ability to withstand blows, flexing or abrasion. Handle prints with both hands and proper support and go slowly.
    • When removing prints from corners, the tape holding the corners should be carefully cut with a scalpel to avoid the risk of damaging the print by bending it during removal.
    • Measuring light – hold the meter parallel and close to the print, be careful not to block the light with your body and take several readings.
    • Light levels for display – use tungsten incandescent lights
  1. 50 lux (5 foot candles) for:
  • a. Salted paper prints
  • b. Albumen
  • c. Platinotypes
  • d Gum Bichromate
  • e. Carbon prints
  • f. Photomechanical prints
  • g. All prints with applied color
  1. 100 lux (10 foot candles):
  • a. Gelatin printing out papers
  • b. Collodion printing out papers
  • c. Gelatin developing out papers (B&W prints)

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