Imagine a photograph that doesn’t look quite like a photograph. It possesses the structure and detail captured by a lens, yet it breathes with the texture, colour depth, and subtle imperfections of a watercolour painting. This captivating hybrid exists in the realm of alternative photographic processes, and one of its most expressive forms is Gum Bichromate printing. It’s a technique born in the mid-19th century, cherished by Pictorialist photographers aiming to elevate their craft to fine art, and still practiced today by artists drawn to its hands-on nature and unique aesthetic potential.
At its core, gum bichromate is a contact printing process. This means the negative used must be the same size as the desired final print. Unlike silver gelatin printing, which relies on metallic silver embedded in gelatin, gum bichromate uses pigments – the very same used in watercolour or gouache paints – suspended in a binder of gum arabic. This mixture is made light-sensitive by adding a dichromate salt, typically ammonium or potassium dichromate. When coated onto paper and exposed to ultraviolet (UV) light through a negative, the magic begins.
The Alchemy of Light, Gum, and Pigment
The process itself is a delicate dance between chemistry, light, and manual skill. It offers considerable control at each stage, allowing for immense artistic interpretation, but also demanding patience and a willingness to embrace unpredictability. Let’s break down the fundamental steps:
Mixing the Sensitiser
The heart of the print lies in the emulsion created by the artist. This typically involves three key ingredients:
- Gum Arabic: A natural gum harvested from acacia trees, it acts as the binder, holding the pigment to the paper. It comes as a liquid solution or powder to be dissolved.
- Pigment: Watercolour paints (tubes or dry pigments) provide the colour. The choice of pigment directly influences the final image’s hue, saturation, and transparency. Artists can mix pigments to achieve custom colours.
- Sensitiser: Ammonium or potassium dichromate solution is added to the gum-pigment mixture shortly before coating. This makes the gum arabic sensitive to UV light. The ratio of sensitiser affects the print’s contrast and speed.
The precise ratios of these components are not rigidly fixed; variations allow artists to fine-tune contrast, density, and colour saturation, contributing significantly to the final print’s character.
Coating the Paper
A suitable paper is crucial, usually a heavy, well-sized watercolour or printmaking paper that can withstand repeated soaking without falling apart. The light-sensitive gum mixture is brushed onto the paper, ideally under subdued tungsten light, as the emulsion is primarily sensitive to UV. Even application is often desired, but deliberate brushstrokes can be left visible to enhance the painterly effect. The paper must then be dried thoroughly in complete darkness.
Exposure
Once dry, a large-format negative is placed directly onto the coated paper, often secured in a contact printing frame. This sandwich is then exposed to a UV light source. Traditionally, sunlight was used, requiring careful monitoring. Today, controlled UV exposure units are common. The UV light passes through the clearer parts of the negative (shadow areas of the final print) and hardens the sensitised gum arabic beneath. Where the negative is denser (highlight areas), less UV light passes through, and the gum remains relatively soft and water-soluble.
Development
This stage is perhaps the most ‘painterly’ and offers significant room for manipulation. Development simply involves immersing the exposed print in a tray of room-temperature water. The unhardened gum (corresponding to the highlights) gradually dissolves, washing away along with its pigment, revealing the paper beneath. The hardened gum (shadows and mid-tones) remains adhered to the paper. Development can be passive – simply letting the print float – or active. Artists might gently agitate the water, use soft brushes, sponges, or even directed streams of water to selectively remove more or less gum, subtly altering tones and textures. This hands-on ‘washing’ phase is where the image truly emerges.
Handle with Care: Dichromate salts (ammonium and potassium dichromate) are toxic and potentially carcinogenic. Always handle them with appropriate safety precautions, including gloves and good ventilation. Avoid skin contact and inhalation of dust. Proper disposal according to local regulations is essential.
Embracing Painterly Expression
What truly sets gum bichromate apart is its inherent capacity for painterly effects. This isn’t merely a byproduct; it’s often the primary attraction for artists using the process.
Unbounded Colour Palette
Unlike the fixed tones of traditional black and white photography, gum printing allows the artist to choose virtually any colour imaginable by selecting or mixing watercolour pigments. Prints can be monochromatic in subtle earth tones, vibrant single hues, or built up in multiple layers of different colours for duotone, tritone, or full-colour effects.
The Power of Layering
Perhaps the most significant technique for achieving depth and complexity is multiple printing. A single exposure rarely yields a full tonal range or sufficient density. Artists typically apply multiple layers of sensitised gum, exposing the same negative (or different separation negatives for colour work) in careful registration each time. Each layer can use a different colour or density formulation. For example, a yellow layer might establish highlights, a magenta layer the mid-tones, and a cyan layer the shadows, building up a rich, full-colour image with a unique texture unlike any other photographic process. This layering inherently mimics the glazing techniques used in painting.
Texture and Surface
The final print surface retains the texture of the paper, influenced by the thickness of the gum layers and the pigment used. Brushstrokes from the coating stage can remain visible. Manipulation during development can create unique marks and softening effects. The result is a tactile object, not just an image, bearing the clear imprint of the artist’s hand.
Atmosphere and Softness
Gum prints often possess a characteristic softness. This isn’t necessarily a lack of detail but rather a gentle rendering of tones and edges, partly due to the nature of pigment particles suspended in gum and the potential for slight diffusion during exposure and development. This quality was highly valued by the Pictorialists seeking atmospheric, evocative images rather than sharp, literal representations.
A Legacy Continued
First patented by Alphonse Poitevin in 1855 and refined later in the 19th century, gum bichromate became a favourite tool for photographers like Robert Demachy, Constant Puyo, and Edward Steichen during the Pictorialist movement. They embraced its perceived imperfections and manipulative potential to assert photography as a legitimate art form, distinct from mere documentation. They celebrated the ability to impart personal vision and manual skill into the final print.
While overtaken by simpler, more predictable photographic processes for commercial and amateur use, gum bichromate never truly disappeared. Today, a dedicated community of fine art photographers and printmakers keeps the process alive. They are drawn to its historical resonance, its deliberate pace in an age of instant digital capture, and its unparalleled ability to merge photographic seeing with painterly execution. Each gum print is inherently unique; slight variations in mixing, coating, exposure, and development ensure that no two prints are ever identical, even from the same negative.
Challenges and Deep Rewards
Gum bichromate printing is undoubtedly challenging. It requires meticulousness, patience, and a good deal of trial and error. Variables like humidity, water temperature, paper characteristics, and pigment properties can all affect the outcome. Achieving consistent results, especially with multi-layered colour prints, demands practice and careful note-taking. Yet, for those who persevere, the rewards are immense. The process offers a profound connection to the materials and the image-making process. The resulting prints possess a beauty, depth, and tactile presence that stands apart, offering a tangible link between the precision of the camera’s vision and the expressive freedom of the artist’s hand. It remains a vibrant testament to the creative possibilities that exist at the intersection of photography and printmaking.
