Oil Print Process Photography Guide — Gelatin Relief Inking Explained

The oil print is one of the most expressive and controllable photographic printing processes ever devised — a dichromate-based process in which the image is formed by selectively inking a gelatin relief with greasy lithographic ink. It was invented by G. E. H. Rawlins in 1904 and became one of the signature processes of the pictorialist movement, valued for the extraordinary degree of manual control it offered the printer. In the oil print, paper coated with a thick layer of gelatin is sensitised with potassium dichromate, exposed through a contact negative, and soaked in water. The exposed (hardened) gelatin absorbs less water and readily accepts oily ink; the unexposed (soft) gelatin absorbs more water and repels ink. By applying ink with a stiff brush, roller, or brayer, the printer builds up an image with complete control over density, contrast, and local tone — more like painting than mechanical printing. The oil print was the basis for the even more elaborate bromoil process, and understanding it is essential for anyone interested in handmade photographic printing at its most expressive.

History and the Pictorialist Connection

The oil print arrived at the height of the pictorialist movement — a period when photographers sought to establish photography as a fine art by producing prints with the handmade qualities of etchings, lithographs, and paintings. The oil print was perfectly suited to this ambition: it required artistic skill, manual dexterity, and aesthetic judgement. The printer could choose the colour and texture of the ink, emphasise or suppress areas of the image, and produce prints that were as much about the hand of the maker as about the subject. Prominent pictorialist photographers who worked with oil prints include Robert Demachy, Heinrich Kühn, and Edward Steichen. The process was widely exhibited and highly regarded in the salons and exhibitions of the early twentieth century.

Chemistry and Principle

The oil print relies on the differential hardening of gelatin by light in the presence of a dichromate sensitiser. A thick layer of gelatin is coated on paper and dried. The gelatin is then sensitised by soaking in a solution of potassium or ammonium dichromate. After drying, the sensitised gelatin is exposed to UV light through a contact negative. Where the light is strongest (the shadows of the negative, corresponding to the highlights of the subject), the gelatin is hardened — cross-linked by the chromium compounds. Where the light is weaker or absent (the highlights of the negative, corresponding to the shadows of the subject), the gelatin remains soft. After exposure, the paper is soaked in water. The soft, unhardened gelatin swells and absorbs water; the hardened gelatin absorbs much less water. When greasy lithographic ink is applied, it adheres to the drier, hardened areas and is repelled by the wet, swollen areas. The result is a positive image in ink.

Paper Preparation

The paper must carry a thick, even coating of gelatin. Some practitioners use commercially prepared gelatin-coated papers (increasingly rare), while others coat their own. To coat your own paper: use a heavy watercolour paper (300gsm or more) and coat it with multiple layers of photographic gelatin, allowing each layer to dry before applying the next. Four to six layers is typical. The gelatin layer must be thick enough to form a visible relief when differentially hardened. After the gelatin layers are fully dried, the paper is ready for sensitising. Alternatively, the Fresson process and some Japanese papers carry sufficiently thick gelatin coatings for oil printing without additional preparation.

Sensitising, Exposure, and Soaking

Sensitise the gelatin-coated paper by soaking it in a solution of potassium dichromate (typically 2-5% in water) for two to five minutes. Remove, drain, and dry in darkness. Expose under UV light through a contact negative — a UV exposure unit, the sun, or UV fluorescent tubes. Exposure should be sufficient to fully harden the gelatin in the highlight areas (the densest parts of the negative). After exposure, soak the paper in cool water for fifteen to thirty minutes. The unhardened gelatin swells with water, while the hardened gelatin resists swelling. The paper is now ready for inking.

Inking: The Heart of the Process

Inking is the creative core of the oil print. Remove the paper from the water and blot off excess surface water. Using a stiff, short-bristled brush (a stipple brush or a small hoghair brush), dab lithographic ink onto the gelatin surface. The ink will adhere to the hardened (drier) areas and be repelled by the swollen (wetter) areas. Build up the image gradually, applying ink lightly and working from the highlight areas toward the shadows. The printer has enormous control: by varying the stiffness of the ink, the pressure and angle of the brush, and the dampness of the gelatin, one can produce results ranging from delicate, subtle tones to bold, graphic effects. Areas can be selectively inked or left light. Multiple inking sessions — alternating inking and re-soaking — can build up density and refine the tonal range. Different coloured inks can be used for different passages of the image, producing multi-colour effects.

Variations and Control

The oil print is perhaps the most manually controllable of all photographic processes. The printer can suppress backgrounds, darken skies, lighten faces, add atmosphere, and create mood through inking technique alone. No two prints from the same negative need be identical — each is a unique interpretation. This quality made the oil print deeply appealing to pictorialist photographers, who prized individuality and artistic expression. The process can produce results that range from photographic realism to near-abstraction, depending on the printer's intent and skill.

The Oil Print Legacy

The oil print process led directly to the bromoil process (which uses a silver gelatin print as the base instead of a dichromate-sensitised gelatin layer) and the oil transfer process (in which the inked relief is transferred to another sheet of paper). Together, these processes represent the pinnacle of handmade photographic printing — processes where the printer's hand, eye, and artistic judgement are as much part of the image as the camera and lens. Today, the oil print is practised by a small but dedicated community of alternative process printers who value its unique combination of photographic fidelity and manual expression.