Collotype Photography Guide — Continuous-Tone Printing Without Dots Explained

The collotype — also known as phototype, Albertype, or Lichtdruck — is a photomechanical printing process capable of reproducing continuous-tone photographs without the use of a halftone screen. Invented by Alphonse Poitevin in the 1850s and perfected by Joseph Albert in Munich in the 1860s, the collotype was for decades the highest-quality method of reproducing photographs in ink on paper. Unlike halftone printing, which breaks an image into a grid of dots, the collotype transfers a continuous gradation of tone through the natural reticulated grain of a gelatin printing plate — producing results of extraordinary smoothness and fidelity. The collotype was widely used for fine art reproduction, postcards, scientific illustration, and bookwork from the 1870s through the mid-twentieth century. Today, only a handful of workshops worldwide still practise the collotype. This guide explores its history, chemistry, plate preparation, printing technique, and the unique qualities that make it one of the most refined processes in the entire history of photography and printmaking.

Historical Significance

The collotype occupies a unique position between photography and printmaking. It was the first process to combine photographic image formation with mechanical ink-on-paper printing, and it did so with a quality that halftone printing — which eventually replaced it — never quite matched. In its heyday, the collotype was the process of choice for the finest photographic reproductions. Museums, art publishers, and scientific institutions used collotype for books, portfolios, and facsimiles where absolute fidelity to the original was required. The great Japanese woodblock print publisher Benrido in Kyoto (founded 1887) still operates a collotype workshop — one of the last in the world — continuing a tradition of quality that stretches back over a century.

The Principle of the Collotype

The collotype is based on the same fundamental chemistry as the carbon print and the gum bichromate: the light-hardening of dichromated gelatin. A thick layer of gelatin on a glass or metal plate is sensitised with dichromate and exposed to UV light through a photographic negative. The gelatin hardens in proportion to the light received — fully hardened in the highlights (the dense areas of the negative, corresponding to the light areas of the subject), partially hardened in the midtones, and barely hardened in the shadows (the thin areas of the negative). The plate is then washed and damped with a mixture of water and glycerine. The hardened gelatin absorbs less moisture and accepts greasy lithographic ink; the soft gelatin absorbs more moisture and repels ink. This is the same water-repels-oil principle used in lithography. The result is a continuous-tone printing plate — no dots, no screen, just smooth gradation from light to dark.

Plate Preparation

A heavy glass plate (or a thick aluminium sheet) is coated with a thick layer of photographic gelatin mixed with a small amount of dichromate. The coating is applied by pouring or spinning and must be extremely even. The plate is dried slowly in a controlled-temperature oven — typically at around 50°C. As the gelatin dries, it develops a characteristic fine reticulation pattern — a network of tiny cracks or wrinkles that is visible under magnification. This reticulated grain is the key to the collotype's tonal quality: it acts as a natural, irregular "screen" that carries ink in varying amounts depending on the degree of gelatin hardening. Unlike a halftone screen, the reticulated grain is random and organic, producing the smooth, grain-free tonal gradation that distinguishes the collotype from all other forms of ink-based printing.

Exposure and Processing

The sensitised plate is exposed to UV light through a contact negative. Exposure must be precisely controlled — overexposure hardens the gelatin too much, producing a flat print; underexposure leaves the gelatin too soft, producing poor ink acceptance. After exposure, the plate is washed in running water to remove the dichromate and is then conditioned by soaking in a solution of glycerine and water. The glycerine replaces some of the water in the gelatin, producing a stable, dampable surface. The plate is then mounted on the bed of a lithographic press, damped with a glycerine-water solution, and inked with lithographic ink using a roller. Paper is then pressed against the inked plate under heavy pressure, transferring the image.

Printing

Collotype printing is a slow, skilled process. Each impression requires careful damping and inking of the plate, and the printer must constantly adjust the balance of damping and inking to achieve consistent results. A single plate can typically produce between 500 and 2000 prints before the gelatin begins to deteriorate. The printing speed is much slower than offset lithography — perhaps 200-500 impressions per day — making the collotype uneconomical for large print runs. However, for small editions of the highest quality, it is unmatched. The prints produced have a remarkable smoothness and depth — a continuous tonal range from paper white to full ink density, with no visible dot structure even under magnification.

Multi-Colour Collotype

The collotype can be printed in multiple colours using colour separation negatives and successive passes through the press with different coloured inks — typically CMYK (cyan, magenta, yellow, black), but sometimes with additional colours for special effects. Multi-colour collotype was used for the finest art reproductions — the results, with their smooth gradation and absence of dot structure, came closer to the appearance of the original artwork than any other printing process. Some Benrido collotype reproductions of Japanese art are virtually indistinguishable from the originals to the naked eye.

The Collotype Today

The collotype is now one of the rarest printing processes in the world. The equipment is specialised, the skill required is exceptional, and the process is slow and expensive by modern standards. Yet the quality of a collotype print remains unsurpassed — the smooth, continuous-tone rendering, the depth and richness of the ink, and the beautiful surface quality make it an object of extraordinary refinement. For the photographer, the collotype represents the ultimate in photographic reproduction — the closest that mechanical printing has ever come to capturing the full subtlety of a photographic original. It is a process worth knowing, studying, and — for the adventurous — attempting.