Palladiotype Photography Guide — Iron-Palladium Warm-Tone Printing Explained

The palladiotype is an iron-palladium photographic printing process that produces rich, warm-toned images of extraordinary tonal range and permanence. Closely related to the platinotype (platinum print), the palladiotype uses palladium salts instead of platinum to form the metallic image. Palladium prints are characteristically warmer in tone than platinum — ranging from warm brown to chocolate to orange-brown depending on the formulation, paper, and humidity conditions — and are equally permanent. Palladium is a noble metal: it does not oxidise or tarnish, making the palladiotype one of the most archivally stable photographic processes available. The process was developed in the late nineteenth century as an economical alternative to platinum printing (palladium being historically cheaper than platinum), and today it is one of the most popular alternative processes among fine art photographers worldwide. This guide covers the chemistry, sensitiser formulation, paper selection, printing technique, contrast control, toning, and the distinctive aesthetic qualities of the palladiotype.

Relationship to the Platinotype

The platinotype was invented by William Willis in 1873 and patented in 1878. It uses the same fundamental chemistry: an iron(III) sensitiser (ferric oxalate) is reduced by UV light to iron(II), which in turn reduces a noble metal salt to its elemental form. In the platinotype, platinum(II) chloride is the noble metal salt; in the palladiotype, palladium(II) chloride (or sodium palladium chloride, or lithium palladium chloride) takes its place. The processes are essentially identical in technique — the same coating, exposure, and development methods work for both. Many modern practitioners use mixed platinum-palladium solutions, blending the cooler tones of platinum with the warmer tones of palladium to achieve the exact image colour they desire.

Chemistry and Sensitiser

The palladiotype sensitiser consists of ferric oxalate (the photosensitive agent) and a palladium salt (the image-forming agent). Ferric oxalate is prepared by dissolving iron(III) oxalate in a small amount of oxalic acid solution. The palladium salt — typically sodium tetrachloropalladate or lithium palladooxalate — is dissolved separately in distilled water. The two solutions are mixed immediately before coating. Contrast control is achieved by varying the proportion of ferric oxalate to palladium salt, or by adding a small amount of sodium chloroplatinate (to boost contrast) or potassium chlorate (to increase contrast). The Ziatype variation by Richard Sullivan uses lithium palladium chloride and offers particularly fine contrast control through humidity manipulation.

Paper Selection

The choice of paper has a profound effect on the palladiotype. The paper must be internally sized, free of optical brighteners, and able to withstand wet processing. Classic choices include COT 320, Arches Platine, Hahnemühle Platinum Rag, Bergger COT 320, and Stonehenge. Different papers produce significantly different image colours, tonal qualities, and surface textures. COT 320 tends to produce warmer tones; Arches Platine gives slightly cooler results. Testing papers is essential — the interaction between sensitiser chemistry and paper fibres is complex and unpredictable.

Coating and Drying

Mix the sensitiser solutions and apply to the paper under subdued tungsten light (not fluorescent, which contains UV). Coat using a glass rod, foam brush, or Japanese hake brush. Work quickly and evenly — the coating should be uniform with no streaks or puddles. The coated paper is dried in darkness. Drying conditions affect the print: in low humidity, the iron salts crystallise finely, giving sharp, high-contrast results; in higher humidity, the salts remain more mobile, giving smoother, softer results. The Ziatype process exploits this effect deliberately, using humidity as a contrast control variable.

Exposure and Development

Contact print under UV light — a UV exposure unit, sunlight, or UV fluorescent tubes. Use a contact printing frame with firm, even pressure. Exposure times vary from a few minutes to twenty minutes depending on UV intensity and negative density. The palladiotype is typically a developing-out process — the image is only partially visible after exposure and requires chemical development to reach full density. Develop by immersion in a tray of potassium oxalate or ammonium citrate solution. The image appears rapidly — within seconds — and reaches full density in one to two minutes. After development, clear in successive baths of dilute hydrochloric acid (or EDTA) to remove residual iron, then wash thoroughly.

The Palladiotype Aesthetic

Palladiotype prints are warm — characteristically warmer than platinum, with rich chocolate-brown shadows, luminous amber midtones, and soft, open highlights. The image is embedded in the paper fibres (not sitting on top as with a gelatin emulsion), giving the print a matte, tactile quality with extraordinary depth. The tonal range is very long — palladium prints can achieve a full twelve or more stops of tonal separation. The combination of warmth, depth, matte surface, and permanence makes the palladiotype one of the most beautiful and valued printmaking processes in photography. For portraits, landscapes, and still life subjects, the palladiotype produces images of quiet, contemplative beauty.