Ambrotype (Positive Collodion)

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Photographic Materials Conservation Catalog
Photographic Processes
Date: Initiated January 2012
Contributors: Amy Brost; Luisa Casella; Lisa Duncan

The Photographic Materials Conservation Catalog is created and maintained by the Photographic Materials Group of the American Institute for Conservation for the convenience of the membership. The treatments, methods, or techniques described herein are provided for informational purposes. The reader assumes responsibility for any application results or interpretation of information.

Ambrotype (Positive Collodion)

The ambrotype is an under-exposed wet collodion negative on glass that appears positive due to the presence of a dark backing or use of dark glass support. In most instances, the image is varnished and placed in a case for safe-keeping. 19th century ambrotypes were displayed in miniature cases just like daguerreotypes.
The “common ambrotype” is a clear glass support backed with a dark piece of textile, metal, secondary glass or paper, or painted directly onto the back of the image. The “ruby ambrotype” is printed onto a dark glass support that is red when viewed in transmitted light. This technique doesn’t require additional backings. Known examples of ambrotypes printed on yellow or blue glass supports exist, but the occurrence is rare.

Cased ambrotype
Ambrotype half over opaque background, half over light table

Historical Facts
Invented: In 1851, Frederick Scott Archer presented the wet plate collodion technique to the photographic societies. He didn’t patent the technique.
Patented: Although earlier practitioners were producing precursors to the ambrotype, i.e. daguerreotypes without reflection, daguerreotypes on glass, collodion positives, positive pictures on glass, verreotypes, James Ambrose Cutting submitted the first official series of patents in 1854. He coined the word, “ambrotype” from the Greek word for “imperishable”.
Main Period of Use: Popular in North America from 1850 to 1870.
Historic Practitioners: Any daguerreotypist involved in commercial portraiture around 1850 would have dabbled in the production of ambrotypes. One well-known daguerreotypist was Platt D. Babbitt (active 1853-1870).
Contemporary Practitioners:
List of contemporary photographers producing ambrotypes:

Ruby glass ambrotype over light table
Back painted ambrotype over light table

Identification Characteristics
Image layer: Collodion and physically developed silver, usually varnished.
Color: Monochrome (may have applied color)
Support: Glass (possibly backed with dark paint). There may also be a secondary dark textile, metal, glass or paper support.
Analysis: A varnish will fluoresce in UV light. Varnished plates will not show signs of image “tarnish”. Unvarnished plates will exhibit white or red-yellow “tarnish” layers over the image.
See also Cased Photographs.

Process Overview
Ambrotypes are created using a wet-plate printing technique. The plate must be wet for the whole procedure - sensitizing, exposing, developing, fixing, and rinsing. First a glass plate is prepared by filing down the edges so they are smooth. Sometimes an albumen subbing layer was applied to the glass prior to the collodion. Then the collodion is poured to the center and allowed to flow to cover the whole plate. Surface tension and a steady hand keep it from spilling. Once it sets up, the plate is taken into a dark room and placed into a bath of silver nitrate, which sensitizes it. Then the plate is placed into a plate holder (a back for a large format camera). Then the plate is placed in the camera and exposed. It is only sensitive to blue/UV light, so artificial blue-light sources are helpful, and sunlight is effective.
The result is a laterally reversed image of the original scene.
The camera back is taken into the darkroom and a shot-glass of developer is poured onto the surface and must be poured evenly or defects result. After about 30 seconds, the plate is rinsed. It is fixed in hypo or potassium cyanide to dissolve the remaining unexposed silver salts.
A varnish (usually shellac or copal, but commonly a "home-brew" of many components) is applied to protect the image.
Coloring may be applied over the image layer using dry pigments.
Cuttings original patents in 1854 called for sandwiching the plate between another piece of glass, so these particular images were not finished in the same way as many.

Conservation and Treatment

Ambrotype with actively flaking backing
  • Flaking of applied dark backing: This can be conservatively addressed by placing a dark secondary support such as black matboard or matboard toned with black carbon pigment, or an exposed and archivally processed matte photographic paper. Areas of loss may also be consolidated. Inpainting can also be done using pigments in acrylic resins, over an isolating layer.
  • Grime on the surface: If unvarnished, the exposed collodion layer is very fragile and should be treated with care. A soft brush can be used. Test any solvents (including water) before use as varnishes, paints and the collodion layer are sensitive to many organic solvents. Even water can dissolve weakened collodion layers. It is best to use non-polar i.e. mineral spirits solvents as most varnishes and the collodion layers are not sensitive. Ethanol and acetone are NOT recommended. The cover glass of an ambrotype, when present, can be separately washed in water/ ethanol solution or water and Photo-flo followed by ethanol rinse. Let air dry entirely before re-sealing against ambrotype to avoid condensation.
  • Broken glass: The image can be repaired with adhesives that do not contain polar solvents. Testing should be done before use. There are also passive techniques for housing an ambrotype without repairing the glass. Consider looking at conservation literature on housing broken glass plate negatives.
  • Soft or cracked image layer: Glass that was improperly manufactured is susceptible to “glass disease”. Ambrotypes printed on this diseased glass will exhibit soft or cracking collodion and/or varnish layers. There is no easy fix for this problem as it’s inherent. Get good digital captures of the image and protect it from sticking to dust and other storage materials.

Housing and Storage
The ambrotype glass support is extremely fragile. 19th century ambrotypes housed in cases are considered composite in nature (glass, wood, leather, paper, adhesives) and should be stored in an environment that doesn’t fluctuate and is kept at around 68F and 45% RH. Freezing is not recommended as any condensation on the plate during thawing may be catastrophically damaging. Loose ambrotypes (not in original cases) are particularly susceptible and should be placed in custom-made rigid enclosures.

Emergency Recovery
If ambrotype is in case and suffered water damage, remove from case and air dry.
Avoid touching the image layer surface.
Freezing is not recommended as any condensation on the plate during thawing may be catastrophically damaging.

See also Cased Photographs bibliography


  • Duncan, Lisa, 2009."Technical Study of Five Ruby Ambrotypes". Unpublished. Available for download at:
  • Hendriks, Klaus B., with Brian Thurgood, Joe Iraci, Brian Lesser, Greg Hill. 1991. Fundamentals of Photograph Conservation: A Study Guide. Toronto, Ontario: Lugus Publicationsfor the National Archives of Canada.
  • King, Chris. 1978. "My Grandmother has One of Those—Daguerreotypes, Ambrotypes, Tintypes—TheirProblems, Processes and Care," Conference of Students in Art Conservation, April 10-12, 1978, pp. 82-97.
  • Lavedrine, Bertrand (with Jean-Paul Gandolfo, John McElhone, and Sibylle Monod). 2007 (French version), 2009 (English Version).
  • Moor, I. 1976. "The ambrotype—research into its restoration and conservation Part 1". The paper conservator. 1: 22-25.
  • Moor I. 1976. "The ambrotype—research into its restoration and conservation Part 2". The paper conservator 2: 36-43.
  • Norris, Debbie. 1983. "The Proper Storage and Display of a Photographic Collection". Paper presented to the Washington Conservation Guild, March 1983. Available at:
  • Photographs of the Past: Process and Preservation. Los Angeles, CA: The Getty Conservation Institute.
  • Reilly, James M. 1986. Care and Identification of Nineteenth-Century Photographic Prints. Rochester, NY: Eastman Kodak.
  • Whitman, Katherine. 2007. "The History and Conservation of Glass SUpported Photographs". Fellowship capstone research of the Advanced Residency Program. George Eastman House. Available at:,_Katharine._%22The_History_and_Conservation_of_Glass_Supported_and_Protected_Photographs.%22#Wet-plate_Collodion_on_Glass

Process and Historic Material

Contemporary Practice

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