Step away from the crisp, digital perfection of modern photography for a moment and delve into a world where light, pigment, and paper conspire to create images with a uniquely tactile and painterly quality. This is the realm of gum bichromate printing, a historical photographic process dating back to the mid-19th century. It’s less about capturing a perfect replica of reality and more about interpreting it, offering artists a remarkable degree of control over the final print’s appearance, texture, and color.
Unlike silver gelatin prints or digital outputs, gum bichromate prints possess a distinct softness and depth. They often resemble watercolors or pastels more than traditional photographs. This aesthetic made the process incredibly popular during the Pictorialist movement of the late 19th and early 20th centuries, when photographers sought to elevate photography to the status of fine art by emphasizing beauty, tonality, and composition over mere documentation.
The Heart of the Process: How It Works
The magic of gum bichromate lies in a relatively simple photochemical reaction. The core ingredients are gum arabic (a natural gum derived from the acacia tree), a watercolor pigment (providing the color), and a dichromate salt (typically ammonium or potassium dichromate). When these are mixed together and coated onto paper, the dichromate makes the gum arabic sensitive to ultraviolet (UV) light.
Here’s the crux: when exposed to UV light through a negative, the areas of the gum arabic layer hit by the light harden in proportion to the amount of light received. The dense areas of the negative block UV light, leaving the gum underneath soft and soluble. The clear areas of the negative allow UV light through, hardening the gum beneath them. After exposure, the print is gently ‘developed’ by washing it in cool or lukewarm water. The unhardened gum arabic, along with the pigment it holds, washes away, while the hardened, light-struck areas remain, forming the image. The pigment is literally trapped within the hardened gum, bonded to the paper fibers.
Materials and Preparation
Successfully creating a gum print requires careful preparation and the right materials. It’s a hands-on craft from start to finish.
Paper: The choice of paper is crucial. It needs to be robust enough to withstand multiple coatings and soakings in water without falling apart. Heavyweight, archival watercolor papers (like Arches, Fabriano, or Rives BFK) are favorites. Critically, the paper must be sized, either internally by the manufacturer or externally by the artist using gelatin, starch, or a synthetic size. Sizing prevents the pigment from sinking too deeply into the paper fibers and staining, ensuring cleaner highlights and better control during development.
Gum Arabic: Usually purchased as dried crystals or powder, it needs to be dissolved in distilled water to create a thick, syrupy solution. Straining it through cheesecloth removes impurities.
Pigments: Artist-quality watercolor tube paints or dry pigments work well. The choice of pigment directly determines the color of the print layer. Richly colored, finely ground pigments generally yield the best results.
Sensitizer: Ammonium or potassium dichromate is dissolved in distilled water to create a saturated solution. This is the light-sensitive component. It’s crucial to handle dichromates with care as they are toxic.
Safety First! Dichromate salts (both ammonium and potassium) are toxic and potential carcinogens. Always wear gloves (nitrile is recommended) when handling the sensitizer solution or the wet emulsion. Work in a well-ventilated area and avoid ingesting or inhaling the powder or solution. Proper disposal according to local regulations is essential.
Negative: Gum printing is a contact printing process, meaning the negative must be the same size as the desired final print. Enlarged digital negatives printed onto transparency film are commonly used today, although traditional large-format film negatives work perfectly too. The negative needs good density and contrast, often requiring adjustments specifically for the gum process.
UV Light Source: The sun is the traditional, free UV source, but exposure times can be variable. Artificial UV exposure units, like those used for screen printing or specialized graphic arts lamps, offer more consistency and control.
Crafting the Gum Print: Step-by-Step
While variations exist, the basic workflow for a single-color gum print follows these stages:
- Sizing the Paper: If not using pre-sized paper, apply a sizing agent (like hardened gelatin) and allow it to dry completely. This might take a day or two.
- Mixing the Emulsion: This is done under low light or safelight conditions. Measure out specific amounts of gum arabic solution, pigment, and dichromate sensitizer. The ratios affect contrast and density; experimentation is key. Mix thoroughly but gently to avoid air bubbles.
- Coating: Pour a small amount of the emulsion onto the sized paper. Using a soft brush (like a hake brush), spread the emulsion evenly across the paper surface in smooth, overlapping strokes. The goal is a thin, even layer.
- Drying: Hang the coated paper to dry completely in total darkness. A fan can speed this up, but avoid heat. The paper is now light-sensitive.
- Exposure: Place the negative (emulsion side down) directly onto the coated paper surface. Sandwich them in a contact printing frame under glass to ensure tight contact. Expose to a UV light source. Exposure times vary greatly depending on the light source intensity, negative density, emulsion mixture, and desired effect – ranging from a few minutes under strong sun to an hour or more with some artificial lights. Determining the correct exposure often requires test strips and experience.
- Development: After exposure, gently slide the print face down into a tray of cool or room-temperature water. Do not agitate vigorously initially. Allow it to soak; the unexposed, unhardened gum and pigment will slowly dissolve and float away. Development time can range from minutes to an hour. Gentle manipulation with water movement or a soft brush can be used towards the end to clear specific areas, offering significant artistic control.
- Clearing (Optional but Recommended): A brief bath in a clearing agent like sodium metabisulfite can help remove any residual yellow dichromate stain, especially if using potassium dichromate. Rinse thoroughly afterwards.
- Drying: Hang the finished print to dry. It may curl, but can be flattened later under weight.
The Aesthetic Appeal and Creative Potential
What makes artists endure this meticulous, sometimes frustrating process? The answer lies in its unique aesthetic and the unparalleled control it offers.
Painterly Quality: Brushstrokes from the coating stage often remain visible, embedding the artist’s hand directly into the photographic image. The way pigments sit within the gum on the textured paper surface inherently lends a non-photographic, painterly look.
Color Control: By choosing different watercolor pigments, artists can print in virtually any color imaginable, moving far beyond the monochrome constraints of many traditional processes.
Multi-Layering: This is where gum bichromate truly shines. Artists can create full-color images by applying multiple layers of emulsion, each with a different color pigment (typically cyan, magenta, and yellow, plus black for depth), exposing each layer with appropriately separated negatives. Each layer requires recoating, re-registering the negative precisely, re-exposing, and re-developing. This multi-layer technique allows for subtle color blending and depth unattainable in a single pass.
Manipulation during Development: The wet development stage is an opportunity for direct intervention. Artists can use brushes, sponges, or directed streams of water to selectively remove more or less emulsion, altering tonality, softening edges, or emphasizing textures.
Verified Fact: The gum bichromate process was patented by Alphonse Poitevin in 1855, but it was John Pouncy who significantly improved its practicality for pigment printing around 1858. Later, figures like Robert Demachy became renowned masters of the process during the Pictorialist era. Its ability to suppress detail and emphasize mood aligned perfectly with Pictorialist ideals.
Texture and Surface: The final print retains the texture of the paper, enhanced by the layers of hardened gum and pigment, giving it a physical presence quite unlike smooth photographic papers.
Gum Printing Today
Despite the advent of digital technology, gum bichromate printing maintains a dedicated following among fine art photographers and printmakers. It represents a deliberate move towards slower, more craft-based image making. The process demands patience, precision, and a willingness to embrace variability and imperfection – each print is truly unique.
Workshops and online resources have made the process more accessible, although the safety precautions regarding dichromates remain paramount. For those seeking a photographic medium that blends photographic capture with painterly expression and hands-on control, gum bichromate offers a deeply rewarding, albeit challenging, path. It’s a testament to the enduring allure of creating images by hand, transforming light, chemistry, and pigment into tangible works of art.
