Vintage photographs from the 19th and early 20th centuries often have a distinctive reddish-brown tone. This tone is the result of the photographic processes and materials used at the time. Understanding the chemistry behind early photography helps explain why old photos have that recognizable antique look.
The Development of Early Photographic Processes
The first successful form of photography was the daguerreotype, introduced in 1839. The daguerreotype process produced a direct positive image on a silver-plated copper sheet. The image was developed using mercury fumes and stabilized with salt. This resulted in photographs with a mirror-like surface and a bold, dark appearance.
Later innovations like the ambrotype and tintype also used photographic plates made of silver-coated copper. The wet plate collodion process, introduced in the 1850s, required photographers to coat glass or metal with light-sensitive chemicals immediately before exposure. The results were photographic negatives on glass that had to be carefully stored in dark slide holders.
Printing photographs from negatives was accomplished through the albumen process. This involved treating paper with a mixture of egg whites and salt, then sensitizing it with silver nitrate. When the negatives were placed in contact with albumen paper and exposed to light, the result was black and white photographs with a glossy or matte surface.
The Cause of Sepia Toning
During the decades when processes like daguerreotypes, ambrotypes, and albumen prints were the leading forms of photography, most photographs ended up with reddish-brown tones. This coloration occurs due to the effects of oxidation and aging on the silver in the photographic emulsion.
Silver is the key component that allows an invisible photographic latent image to be rendered visible. When the developed silver particles are exposed to humidity, air pollution, and light over time, the silver oxidizes. This causes the black and white photographic image to take on a reddish-brown, sepia hue.
The tone can range from light tan to deep chocolate brown. Images made on silver-coated copper plates develop stronger sepia tones over time compared to albumen prints on paper.
The Chemistry of Sepia Toning
Oxidation is the primary mechanism by which sepia toning occurs in old photographs. Oxygen reacts with the metallic silver in the emulsion, converting it to silver oxide or silver sulfide compounds. These oxidized forms of silver are more transparent than pure black silver metal, causing the image to fade to a brown tone.
Pollutants like sulfur dioxide in the air can speed up the sepia toning over decades. Photographic emulsions also naturally contain residual iron from manufacturing. Iron acts as a catalyst for oxidizing silver through a process called redox chemistry.
Besides oxidation, sepia toning is enhanced by yellowed varnish on the image surface. Nearly all vintage photos were coated to protect the emulsion and provide a richer tone. As the varnish ages, it tends to yellow or darken further, adding a warmer tone to the underlying sepia photograph.
The Purposeful Use of Sepia Toners
In addition to natural sepia toning over time, photographers in the late 1800s and early 1900s would intentionally treat prints with sepia toner chemicals. Toners were used for several reasons:
- Darken the image for richer blacks and browns
- Provide archival protection for the silver image
- Give a uniform antique tone to the photograph
Potassium ferricyanide became a common chemical toner to convert silver to sepia shades. The photographer could control the toner strength for subtle to dramatic sepia effects.
Modern Creative Uses of Sepia Toning
Even in today’s digital photography world, sepia toning remains a popular special effect. Photo editing software makes it easy to convert color or black and white images to sepia.
Creative uses of digital sepia toning include:
- Vintage or retro aesthetic
- Nostalgic effect
- Warm, romantic feel
- Antique newspaper or manuscript look
- Selective toning to highlight specific areas
Sepia toning can be applied uniformly or with variations such as lighter, darker, warmer, or cooler tones across an image.
Examples of Sepia-Toned Photographs
Here are some iconic photographs exhibiting natural or intentional sepia toning:
| Photograph | Photographer | Year | Notes |
|---|---|---|---|
| An Old Negro Man | Thomas Easterly | circa 1850s | Daguerreotype photograph naturally toned sepia over time. |
| Oscar Wilde | Napoleon Sarony | 1882 | Albumen silver print likely toned sepia to protect the image. |
| Migrant Mother | Dorothea Lange | 1936 | Gelatin silver print digitally converted to sepia tone. |
Distinguishing Natural and Artificial Sepia
How can you tell if an old photograph’s sepia tone is natural aging versus intentional toning?
Clues that sepia is artificial include:
- Uniform tone across the image
- Richer, darker brown than usually occurs with aging
- Photograph is printed on modern resin-coated paper
- Warm tone but black densities are strong
Signs of natural sepia toning over time:
- Uneven sepia tones across image
- Highlights, borders and margins lighter than rest of image
- Weakened image density and detail
- Presence of silver mirroring or oxidation spots
Assessing these visual clues along with the print process and paper type can help identify sepia that developed over decades versus intentional toning.
Conclusion
The distinctive reddish-brown tone of vintage photographs is caused by the natural oxidation and deterioration of silver particles in the emulsion. Silver reacts with oxygen, humidity, and pollutants over time to produce sepia tones through a process called oxidation. Photographers also intentionally toned prints with sepia for aesthetic effect and archival stability. Sepia remains a beloved effect for digitally manipulating modern photos.
By Brian Scott, March 3, 2023