Printing-Out Paper (POP) Photography Guide — Self-Masking Silver Printing Explained

Printing-out paper (POP) is a class of photographic printing materials in which the image appears directly during exposure to light, without chemical development. Unlike developing-out paper (DOP), which requires immersion in a chemical developer to reveal the latent image, POP produces a visible image through the direct photolytic reduction of silver salts by light. The image "prints out" — it appears gradually as the paper is exposed under a contact negative in sunlight or UV light. Printing-out papers were the dominant photographic printing materials of the nineteenth century: salted paper, albumen paper, collodion POP, and gelatin POP all belong to this family. Commercially manufactured gelatin POP survived well into the twentieth century and is still available in limited quantities today. POP prints have a characteristic warmth, smoothness, and tonal subtlety — with self-masking highlight exposure that produces beautiful, open highlights and rich shadow detail. This guide covers the history, chemistry, technique, toning, and aesthetic qualities of printing-out paper.

History of Printing-Out Papers

The earliest photographic prints — Talbot's "photogenic drawings" of 1834 — were printing-out images: paper sensitised with silver chloride and exposed in sunlight until the image appeared. Salted paper prints (1840s), albumen prints (1850s-1890s), and collodion POP (1880s-1900s) were all printing-out processes. The image forms by the direct reduction of silver halide to metallic silver by photons. Because the silver particles formed by direct photolysis are extremely small, POP images have a warm, brownish-purple colour before toning — quite different from the neutral-to-cool black of developed silver images. Gold toning (standard practice for all POP materials from the 1850s onward) shifts the colour to a richer, more stable purple-brown and greatly improves permanence.

Chemistry of Printing Out

In a printing-out emulsion, silver chloride (or silver chlorobromide) is the light-sensitive compound. When photons strike a silver chloride crystal, the energy breaks the ionic bond, freeing a silver ion and a chloride ion. The silver ion is reduced to a metallic silver atom. Unlike developing-out processes — where just a few atoms form a latent image that is amplified by millions during development — POP relies on continued photolysis to build up enough metallic silver for a visible image. This means POP is much slower than DOP, but it also means the image is self-masking: the silver already deposited in the highlights absorbs some of the incoming light, slowing further exposure in those areas. This self-masking effect gives POP prints their characteristic long tonal range and open, luminous highlights.

Contact Printing Technique

POP is a contact printing material — the negative must be the same size as the desired print. Place the negative in firm contact with the POP in a contact printing frame (a hinged-back frame with a glass front). Expose in sunlight or under UV light. The image appears gradually. The printing frame has a split back that allows you to open one half and check the progress of the print without disturbing the registration of negative and paper. Print until the darkest areas are slightly darker than you want in the final print — fixing and toning will lighten the image slightly. Exposure times vary from a few minutes in strong sunlight to an hour or more in overcast conditions.

Toning and Fixing

After printing, POP must be toned and fixed. Toning is typically done before fixing to produce the most stable and beautiful results. Gold toning — immersion in a dilute gold chloride solution — is the classic treatment. Gold toning converts some of the photolytic silver to gold-silver alloy, shifting the image colour from raw brownish-purple to a rich, warm purple-brown and greatly improving lightfastness and archival stability. After toning, the print is fixed in sodium thiosulphate to remove unexposed silver chloride, then thoroughly washed. Selenium, platinum, and palladium toners can also be used, each producing different colour and permanence characteristics.

The POP Aesthetic

POP prints have a visual character that is distinct from developed (DOP) prints. The self-masking exposure produces a naturally long tonal scale — open highlights that glow, smooth midtones, and rich, detailed shadows. The image colour (after gold toning) is warm — purple-brown to chocolate — quite different from the neutral black of a developed gelatin silver print. The surface of gelatin POP is typically glossy and smooth, giving the image a jewel-like clarity. Albumen POP has a similar warmth with a slightly different surface texture. The overall impression is of warmth, luminosity, and refinement — qualities that made POP the preferred printing material for portrait photographers from the 1860s through the early 1900s.

Modern POP and Revival

Commercially manufactured POP is still available in limited quantities — notably from specialist suppliers. Some practitioners make their own POP by coating paper with a silver chloride emulsion in gelatin. The resurgence of interest in historical and alternative photographic processes has brought POP back into active use among fine art photographers who value its unique tonal qualities and warm colour. For photographers working with large-format negatives, POP offers a direct, intimate connection to the light that made the negative — the print is literally a record of sunlight passing through the negative and acting on the silver in the paper.