I was showing my calotypes to a group of friends recently and one of them asked why my calotypes varied in color from a near neutral tone to very rich and deep warm browns/reds.
The others in the group were fascinated by my explanation and mentioned this would make for a good article on my blog. So, here I am.
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Look at the calotype on the left and the one on the right. Then, read my explanaiton below and share your thoughts about these two calotypes in the comments section below.
Exposure time and lighting conditions are critical in shaping the color and tone of calotype paper negatives. Color refers to the hue or tint of the calotype (e.g., neutral, warm brown, red/brown), while tone describes the value, or the lightness and darkness of the image, independent of its color. The density of the calotype, which impacts the richness and contrast within the image, is also considered an aspect of tone. Adjustments in exposure time and changes in lighting conditions can lead to variations in color and tone, influencing the overall aesthetic and visual impact of the calotype.
Here’s how each factor can impact the final appearance:
Exposure Time
- Longer Exposures: When you expose your calotype for a longer duration, more silver halides are reduced, leading to greater density in the negative. This can result in richer and sometimes warmer tones due to the more developed silver deposits. Overexposure may push the color toward deeper warm browns as the silver build-up reaches saturation.
- Shorter Exposures: If the exposure time is too short, the negative may be underdeveloped, resulting in less dense silver deposits. This can yield a lighter, less saturated tone that may lean toward neutral or cooler shades, especially if development doesn’t fully compensate for the exposure.
Lighting Conditions
- Direct Sunlight: Natural sunlight, particularly when direct and intense, can influence the reaction of the silver halides in the iodized paper. The high UV content in sunlight can speed up the exposure, leading to more active reduction of silver halides, often producing warmer, more vibrant tones.
- Diffused or Indirect Light: When the light is softer or indirect (e.g., on overcast days or with shaded areas), the exposure tends to be slower and more controlled. This can result in a more even exposure and, in some cases, less intense tonality that might appear cooler or more neutral.
- Quality of Light (Warm vs. Cool): The color temperature of the light (measured in Kelvin) can subtly influence the tone of your calotypes. Warmer light (e.g., morning or late afternoon sunlight) tends to push the resulting print toward warm brown tones. Cooler light (e.g., midday or shaded areas) may produce more neutral or slightly cooler hues in the final print.
The calotype on the left was exposed early in the morning, while the one on the right was exposed to direct sunlight. The calotype on the left was purposely underexposed, a little less than I normally would for these lighting conditions. Both were fixed with TF-4 and processed using my standard workflow. I used my Dallmeyer 3B lens for both calotypes, wide open at f/3.
Summary of the Impact:
Exposure time determines the amount of silver that reacts during the exposure, directly affecting the density and saturation of the image. A longer exposure generally leads to warmer and richer tones, while shorter exposure may result in less dense, potentially cooler-toned negatives. The lighting condition affects how evenly and at what intensity the silver halides are exposed, with natural variances in light quality (warm or cool) impacting the overall color and tone of the final print.
Adjusting and being mindful of these factors can help you achieve more consistent results or purposefully use them to create specific aesthetic effects in your calotype work.
The Choice of Fixer Type Matters
I did not mention this to my friends the other day, but I thought about this while I was writing this article. The choice of fixer and its temperature can significantly influence the final color and tone of calotype prints due to how these factors interact with the silver image and remaining chemicals. Here’s an explanation of why these changes occur:
Type of Fixer (TF-4 vs. Sodium Thiosulfate)
- TF-4 (Alkaline Rapid Fixer): TF-4 is an alkaline fixer that works faster than traditional sodium thiosulfate fixers. Because it is alkaline, it minimizes the loss of image density and can help preserve warmer tones in the silver image. This fixer may leave the calotype with a warmer, richer appearance, as it does not bleach the silver as much during the fixing process.
- Sodium Thiosulfate (Traditional Fixer): Sodium thiosulfate is a neutral or slightly acidic fixer that typically takes longer. It may interact more with the silver halides, potentially leading to a subtle bleaching effect. Depending on how long the print is left in the fixer and how thoroughly it is washed afterward, this can shift the tone of the print toward more neutral or cooler colors.
Fixer Temperature (20°C to 40°C)
- Room Temperature (20°C): When the fixer is used at room temperature, the reaction rate is slower, which allows for more gradual fixing and potentially preserves the integrity of warmer tones. This slower process can help retain some of the calotype’s natural color characteristics.
- Warmed Fixer (40°C): When the temperature of the fixer is increased, the fixing reaction accelerates. This higher temperature can increase the solubility of silver compounds, sometimes leading to a more aggressive interaction with the image. The warmer temperature can result in slight bleaching, affecting the density and potentially shifting the tone toward more neutral or cooler hues. Additionally, faster chemical reactions at higher temperatures can change how the silver image interacts with any residual halides, altering the overall tonality.
Why These Factors Matter:
- Preservation of Warm Tones: TF-4, being alkaline and faster-acting, tends to preserve warmer, richer tones due to less interaction with the image silver.
- Shift to Neutral or Cooler Tones: Sodium thiosulfate, particularly when used at higher temperatures or for extended periods, can remove more unreacted silver, potentially leading to a lighter, more neutral appearance.
- Temperature Influence: Higher temperatures generally accelerate all chemical reactions, which can amplify the effect of the fixer on the image, shifting tones due to more extensive interaction with the silver deposits.
These variables in your fixing process contribute to the nuanced tonal changes in your calotypes, offering you creative control over the final appearance of your negatives by adjusting the type of fixer and its temperature.
You might be wondering, since calotypes are typically used as negatives to create prints, why should their appearance matter unless it directly impacts the printing process? Over time, I found myself increasingly drawn to the unique beauty of my calotype paper negatives. The more I studied them, the more I appreciated their character and detail, leading me to consider mounting and displaying them as final works of art. While this approach may not be suitable for every piece, I find myself appreciating it more with each passing day.
Look at the two calotype paper negatives below. The one on the left was fixed with sodium thiosulfate (hypo) at 40C and the other with rapid fix (TF-4) at 20C. Both were exposed in natural light for similar times and at about the same time of day.
If I were planning on displaying these calotypes as the final artwork, depending on the narrative and artist statement, these differences could be substantial.
As a creative professional, maintaining complete control over my workflow is essential. I need the confidence and skill to guide and shape my work in any direction I choose. This autonomy ensures that my artistic vision is fully realized and allows me to adapt and refine my process as needed.
Darkroom Diary Premium Members receive exclusive access to my technical notes, presentations, videos, and chemistry notes used to create handmade calotype paper negatives, wet plate collodion negatives, and salt prints.
Consider becoming a premium member to support my monthly creative and technical articles and videos dedicated to analog photography. Your membership directly helps me continue publishing unique, high-quality content exclusively for analog photography enthusiasts like you.
