Archival Stability and Conservation of Salt Prints

The salted paper print, one of the earliest photographic printing processes, was introduced by William Henry Fox Talbot in the 1830s. As a positive printing method derived from paper negatives, it quickly gained popularity for its simplicity and ability to produce beautiful, tonal images. However, despite their aesthetic appeal, salt prints have long been plagued by issues of impermanence. The very nature of the process—using finely divided silver particles embedded within paper fibers—renders the prints vulnerable to environmental pollutants, moisture, and chemical instability.

Throughout the 19th century, practitioners and researchers, including Talbot himself, struggled to understand why some prints faded rapidly while others endured. Early photographic societies formed committees to investigate the issue, particularly the infamous “Fading Committee” of 1855, which documented various chemical and environmental factors contributing to degradation. Although many solutions were proposed—such as improving fixing methods, gold toning, and refining paper selection—salt prints often failed to achieve the archival permanence desired by artists and collectors alike.

Modern-day photographers, conservators, and researchers continue to grapple with these challenges. However, historical insights and advancements in photographic conservation make it possible to create salt prints with greatly improved stability and longevity. This report examines the top known issues contributing to the poor archival performance of 19th-century salt prints and outlines the most effective contemporary practices for enhancing their durability. By understanding the failures of the past and applying scientifically tested methods, it is possible to produce salt prints that capture the medium’s beauty and stand the test of time.

Historical Factors Leading to Poor Archival Performance of Salt Prints

Inherent Fixing and Washing Problems: As Dr. Mike Ware observed, “since the inception of the silver salted paper print, its problems have always lain in the fixing – rather than the recording – of the image” [1]. Early salt prints were often poorly fixed and washed, leaving behind light-sensitive silver salts and thiosulfate (“hypo”) residues in the paper. These residual chemicals were the most common cause of image deterioration [2]. If unremoved, leftover silver halides could continue to react or darken, and residual thiosulfate would slowly decompose to release sulfur that attacks the image silver, especially in the presence of moisture [2].

In 1855, the Photographic Society of London’s famous “Fading Committee” concluded that “the most ordinary cause of fading may be traced to the presence of sulphur, the source of which may be intrinsic from hyposulphite [fixer] left in the print, or extrinsic from the atmosphere, and in either case the action is much more rapid in the presence of moisture” [2]. Talbot’s own printer, Henneman, later admitted that prints in The Pencil of Nature had been given only three washings; many of those prints “totally failed” (faded to invisibility) a few years later [3].

The 1855 Fading Committee explicitly cautioned against additives that “had the effect of decomposing the sodium thiosulfate” and thus caused premature sulfiding of the image [2].

Lack of Protective Toning (Untoned Silver Images): The finely divided silver particles in an untoned salt print are chemically very active and prone to oxidation and sulfiding. Gold toning of salt prints was introduced in 1847 to improve image stability and enhance tone [4].

By replacing some of the image silver with gold, or plating gold onto the silver, this treatment made the prints less reactive. However, gold toning did not become widespread until the 1850s when Gustave Le Gray and others strongly recommended it [4].

Use of “Self-toning” or Impure Fixatives: In the mid-19th century, photographers experimented with additives in the fixer to simultaneously tone and fix prints – a practice that sometimes backfired. One common method was sulfur toning via “old hypo.” Photographers noticed that an old, partially decomposed thiosulfate bath would impart a deeper brown tone to prints [5].

Poor Paper Quality and Impurities: The paper support of salt prints was another source of instability. Early salt prints were typically made on whatever drawing paper was available, and the purity of papers in the 1840s varied greatly. Papers containing trace chemicals from manufacturing could react with silver, causing black spots or mottling [6].

Environmental Factors – Humidity, Pollutants, and Light: Even when a salt print was well processed, the external environment played a huge role in its longevity. High relative humidity accelerates almost every degradation pathway. Atmospheric pollutants like hydrogen sulfide (H₂S) and prolonged light exposure could cause rapid deterioration [2][7].

Handling and Physical Abuse: The physical nature of salted paper prints made them vulnerable to mechanical damage and careless handling. Unlike later photograph types, salt prints have no protective binder layer – the silver image resides directly in the paper fibers [8].

Modern Strategies for Improving Stability and Long-Term Preservation of Salt Prints

Materials and Processing

High-Quality Archival Paper: 100% cotton rag paper, acid-free, purified, and free of harmful additives. Papers like Arches Platine 310, Hahnemuhle Platinum Rag, and Rives BFK are commonly used [9].
Optimized Sensitizer Formula: Using silver nitrate sensitizer at 10–12% strength, acidified with citric or acetic acid to prevent unwanted chemical reactions and ensure uniform sensitization [10].
Thorough Fixing and Washing: Multi-step fixing (two-bath process) with fresh fixer followed by extensive washing is crucial for archival quality [11]. Hypo-clearing agents may be used to enhance washing effectiveness [12].
Toning: Gold toning is essential for improved image stability. Gold or platinum toning replaces some silver with more inert metals, making prints less susceptible to atmospheric pollutants and light exposure [4][13].
Coating (Optional): Applying wax or conservation varnish can enhance protection from moisture, pollutants, and handling [14].

Storage and Display

Controlled Environment Storage: Salt prints should be kept in a dry, cool, and clean environment. Ideal conditions are 30–40% RH and temperatures below 20°C [15].
Proper Handling: Always use gloves or handle prints by their edges. Use archival sleeves and mount prints on acid-free boards [16].
Limited Light Exposure: Display only under 50 lux or lower, with UV filtering. Periodic dark storage is recommended for preservation [17].

Fixing Formulas & Workflow Suggestions

Several sources provide specific guidance on fixing formulas and concentrations, as well as recommended fixing times for salt prints.

Here is a summary of the most relevant recommendations:

Reilly, James (The Albumen & Salted Paper Book, 1980)

Reilly discusses that sodium thiosulfate (hypo) was the most commonly used fixer in the 19th century, typically at concentrations of 10–15% (weight/volume).
Recommended fixing time: 10 minutes, but most practitioners used a shorter duration, often leading to incomplete fixation.
Reilly strongly recommends a two-bath fixing process for archival stability. First bath: 10 minutes, followed by a fresh second bath: another 10 minutes. This ensures thorough removal of unexposed silver halides. [2]

Photographic Society of London’s Fading Committee (1855)

They identified that incomplete fixing was a major cause of fading.
Recommended formula: 10% solution of sodium thiosulfate.
Advised a minimum of 10–15 minutes of immersion with thorough agitation to allow proper chemical action. They found that prints inadequately fixed or washed would invariably deteriorate. [3]

Kodak (Processing Chemicals and Formulas for Black and White Photography, 1963)

Provides a formula for a standard sodium thiosulfate fixer:
- Sodium Thiosulfate (anhydrous): 240 grams (or 300 grams if using the pentahydrate form)
- Water to make 1 liter.
- This yields a 24% solution, but the concentration can be adjusted to 10–15% for salt prints to prevent bleaching.
Recommended fixing time: 10 minutes (single bath) or 5 minutes in each bath (two-bath method). [11]

Mike Ware (Mechanisms of Image Deterioration in Early Photographs, 1994)

Ware notes that the use of ammonium thiosulfate (rapid fixer) was occasionally suggested later in the 19th century but was generally avoided because it was believed to bleach the image.
However, a diluted ammonium thiosulfate solution (around 5%) could be used effectively if followed by thorough washing.
For archival stability, Ware endorses two-bath fixing with sodium thiosulfate, each bath for at least 5 minutes. [13]

Ellie Young (The Salt Print Manual, 2011)

Suggests using a 10% sodium thiosulfate solution for most salt prints.
Recommends a two-bath fixing process of 5 minutes in the first bath, followed by 10 minutes in the second bath.
She advises against using old or exhausted fixer as it can contain decomposition products harmful to the print. [12]

PSAP (Preservation Self-Assessment Program)

States that ammonium thiosulfate is generally not recommended for salt prints, but if used, it should be very dilute (5% or lower).
Sodium thiosulfate is preferred, ideally in a two-bath process to ensure maximum hypo removal. [16]

Common Consensus:

Sodium thiosulfate is the preferred fixer, typically at 10% concentration.
A two-bath process is highly recommended for maximum archival stability.
Total fixing time: 10–15 minutes, often divided between two fresh baths (e.g., 5 minutes each or 10 minutes first bath, 5 minutes second bath).
Fresh fixer is essential; reusing fixer is discouraged.

Top 3 Recommendations for Longevity

Based on the research, the top 3 things that will most significantly improve the long-term stability of salt prints made today are:

1. Proper Fixing and Washing (Archival Processing)

Thorough fixing and washing are essential for salt prints’ long-term stability. Historically, incomplete fixing was the most common cause of fading, as residual thiosulfate and silver halides degrade over time, especially in humid conditions.

Best Practices:

Use a 10% sodium thiosulfate solution as the standard fixer (or a highly diluted ammonium thiosulfate solution at around 5% if used).
Apply a two-bath fixing process:
First bath: 10 minutes or 5 minutes (if two-bath method is used).
Second bath: 5–10 minutes in fresh fixer to ensure thorough removal of undeveloped silver salts.
Thoroughly wash prints in running water or with multiple changes for at least 30–60 minutes to remove all traces of thiosulfate.
Use a hypo-clearing agent (e.g., dilute 1& sodium sulfite solution) to enhance washing efficiency and further reduce thiosulfate residues.

This method ensures the removal of all unreacted silver salts and thiosulfate, which are the primary culprits of degradation. This step alone dramatically improves permanence.

2. Gold Toning (Or Platinum/Palladium Toning)

Replacing or protecting the silver image with gold or other noble metals is essential for creating stable, long-lasting prints. Gold toning makes the silver image more chemically inert, reducing its reactivity with atmospheric pollutants, moisture, and light.

Best Practices:

Use gold chloride toning solutions prepared with a mild alkali (e.g., borax or sodium acetate) or ammonium thiocyanate.
Tone after a brief initial fix or after complete fixing—both methods are effective, though toning after partial fixing provides better protection.
Apply toning until the desired color shift occurs (generally purplish-brown or neutral brown), ensuring a sufficient layer of gold is deposited to protect the silver.
Consider platinum or palladium toning for even greater permanence, as these metals are more inert than gold.

Gold or platinum-toned salt prints have been shown to endure far better under adverse conditions than untoned prints.

3. Controlled Environment Storage and Display

Even well-processed prints can deteriorate if stored or displayed in poor conditions. A stable, clean environment is crucial for longevity.

Best Practices:

Keep prints in low humidity environments: 30–40% Relative Humidity (RH) is optimal. Avoid fluctuations and ensure conditions remain stable.
Store at cool temperatures: Ideally below 20°C. Cold storage (e.g., 0–5°C) can be even better for master prints that aren’t frequently accessed.
Use acid-free, archival materials: Paper sleeves, folders, and mounting boards should be acid-free and lignin-free. Ideally, they should pass the Photographic Activity Test (PAT).
Avoid exposure to pollutants: Keep prints away from wood, adhesives, paints, and other sources of sulfur or acidic off-gassing. Use enclosures with activated carbon or molecular sieves if needed.
Minimize light exposure: Display only under low light (50 lux or lower), with UV-filtering glass or acrylic. Rotate prints in and out of display, and avoid prolonged direct sunlight.

Proper environmental control greatly reduces the risk of fading, silver tarnishing, or paper deterioration.

Mounting vs. Acid-Free Sleeves

The choice between mounting salt prints to an acid-free board with a proper mounting tissue (like Gudy 831) or storing them in clear archival sleeves depends on your specific goals for presentation, protection, and long-term stability. Here’s a detailed comparison:

Option 1: Mounting Salt Prints on Acid-Free Board with Gudy 831

Pros:

Structural Support: Mounting provides structural rigidity, preventing warping or curling of the paper.
Enhanced Presentation: Suitable for display or framing, especially for exhibitions or portfolio presentations.
Archival Safety: Using high-quality, acid-free boards with a PAT-tested adhesive like Gudy 831 is generally safe for long-term storage. Gudy 831 is known for being a pH-neutral, pressure-sensitive, acid-free, and PAT-tested adhesive designed for conservation-quality mounting.
Reduction of Physical Damage: Mounting minimizes handling of the print surface, which can help prevent abrasion or damage.

Cons:

Risk of Adhesive Deterioration: Over very long periods, even high-quality adhesives can potentially degrade, especially if exposed to high temperatures or humidity.
Permanent Bond: Mounting is a permanent process, making it difficult to remove the print later without causing damage.
Potential for Chemical Interaction: While Gudy 831 is acid-free and tested for archival use, any adhesive introduces the potential for chemical interaction with the print over many decades or centuries.

Option 2: Storing Prints in Clear Archival Sleeves (e.g., Polyester, Polypropylene, or Polyethylene Sleeves)

Pros:

Non-Invasive: No adhesive or mounting tissue is applied to the print, preserving the original state of the artwork.
Ease of Handling: Clear sleeves protect the print from direct contact during handling, reducing risk of abrasion or contamination.
Long-Term Stability: Archival polyester (e.g., Mylar D or Melinex 516) is highly stable and chemically inert, offering excellent protection against environmental pollutants and moisture.
Reversibility: Prints can be removed from sleeves without any risk of damage, making this method completely reversible.

Cons:

Lack of Structural Support: Prints may warp or curl over time if not properly stored with a supportive backing (e.g., acid-free board placed behind the sleeve).
Static Charge Risk: Some clear sleeves can build up static electricity, which may attract dust or fine particles. This is less of an issue with high-quality archival materials like Melinex or Mylar.
Handling Damage Risk: If the sleeve is not sturdy or properly stored, the print can still be damaged during handling or storage.

Best Practice Recommendation

If long-term preservation and flexibility for future conservation work are your primary goals, storing prints in high-quality archival sleeves is generally preferred. This approach minimizes potential chemical interactions and maintains the print’s original condition.

For the highest stability, use archival polyester sleeves (Mylar D or Melinex 516). Polypropylene or polyethylene sleeves are also acceptable but are less durable.
Store the prints in a cool, dry environment, preferably below 20°C and with relative humidity between 30-40%.
Place each sleeve within a buffered or acid-free folder or box for added protection.

If you want to display or exhibit the prints, mounting with Gudy 831 on acid-free board is a good option, provided you understand that the process is semi-permanent. For best results:

Use a high-quality, acid-free, lignin-free board.
Ensure the mounting environment is clean and free from pollutants.
Avoid displaying prints for extended periods; use UV-filtered glazing and keep light levels below 50 lux.

References

Ware, Mike. On the Stability of Robert Adamson’s Salted Paper Prints. History of Photography, Vol. 27, Issue 1, 2003, p. 38.
Reilly, James. The Albumen & Salted Paper Book. Rochester: Light Impressions Corp., 1980.
Photographic Society of London. Report of the Committee on Fading of Photographs, 1855.
Getty Conservation Institute. Atlas of Analytical Signatures of Photographic Processes: Salted Paper Print. Los Angeles, 2013.
Canadian Conservation Institute (CCI). Care of Black-and-White Photographic Prints.
Preservation Self-Assessment Program (PSAP). Salt Print Entry.
V&A Museum. Salted Paper Prints: Their Past, Present and Future, 2018.
Tim Layton. Salt Prints – Tim Layton Fine Art, 2024.
Photrio Forum Discussions, Kodak/Eastman Research.
Getty Museum & Harvard University. Salted Paper Prints Symposium, 2017.
Kodak. Processing Chemicals and Formulas for Black and White Photography. Rochester: Eastman Kodak, 1963.
Young, Ellie. The Salt Print Manual. Victoria: Goldstreet Studios, 2011.
Ware, Mike. Mechanisms of Image Deterioration in Early Photographs. London: Science Museum, 1994.
Reilly, James. Care and Identification of 19th Century Photographic Prints. Rochester: Eastman Kodak, 1986.
Canadian Conservation Institute.
PSAP.
V&A Museum.

Art Collector Resources

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Collector’s Guide [read]
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Why I Create [read]
Aura – What is it, and why does it matter? [read]
Why Analog Photography Is a Smart Investment [read]
Analog photography in the Digital Age: Examining transformation, alienation and authenticity in modern photographic practice. https://doi.org/10.55927/ijads.v2i3.11019

Archival Stability and Conservation of Salt Prints