Collotype

Collotype is one of the oldest practical photomechanical printing techniques, with a proven ability to preserve images for over a century. For this reason, photographs printed using collotype are still used today in restoration records of Kyoto’s temples and shrines.
Founded in 1887 during the Meiji era, Benrido remains the world’s only workshop capable of producing color collotype prints. Known for projects such as life-size reproductions of the murals in Hōryū-ji’s Golden Hall, Benrido was entrusted with the plate-making and printing of this work.

The current production process employs high-resolution digital cameras, large-format negative film, glass plates, dedicated pigment inks, and collotype printing presses.

From Image Capture to Retouching

Image capture is performed using a high-resolution Phase One camera. This has allowed us to capture even subtle colors and paper textures that cannot be recorded when using a flatbed scanner. In offset printing, the standard method for commercial printing, four CMYK colors and four printing plates are typically used. By contrast, Shueisha Manga-Art Heritage’s art prints are sometimes made using over 20 colors and 20 printing plates, depending on the work.

After separating the colors using software, the parts where different colors overlap are retouched. For example, when a character’s outlines or hair are drawn over skin tones, even minimal plate misalignment can expose the white paper beneath, and the sense of depth created by overlapping colors would be lost if the data were reproduced without adjustments. For this reason, areas left white in the data are retouched by filling them in with the same skin tone. This work cannot be done automatically, so it is all carried out manually by the staff.

Film Output

The completed data is output to large-format negative film at the same dimensions as the final print size. The negatives are checked, and a pencil is used to draw gradients and other details directly onto the negatives in places where finishing touches are deemed necessary.

Glass Plate Production

In Japanese, collotype used to be called hariban, meaning “glass plate” (hari is an archaic word for glass). In this process, a gelatin photosensitive solution is poured onto a glass plate and spread evenly over the surface by tilting it in all directions. The glass plates typically used come in two sizes: one that is 695cm × 455cm × 10mm thick, weighing approximately 9kg, and another that is 1250cm × 720cm × 10mm thick, weighing approximately 24kg. The glass plates are placed for approximately 1hours in a drying chamber adjusted to 60–65°C and about 20% humidity, until they reach a state suitable for plate making.

Exposure

The negative film is placed on the exposure table, a glass plate is set on top, and a rubber sheet is laid over it. The air is removed to ensure close contact, the table is rotated, and ultraviolet light is irradiated from above. Once exposure is complete, the glass plate is taken off the table and rinsed under running water. Minute wrinkles can be seen on the resulting printing plate. In offset, gravure, inkjet, and other such printing methods, colors and lines are formed by groups of small dots. On the other hand, in collotype printing, tonal variation is expressed by the amount of ink held within these wrinkles. A defining feature of collotype printing is the smooth gradations, where no halftone dots are seen, even when viewed under magnification.

Printing

Benrido operates 4printing presses made by Mitani (Aichi) and one large-format printing machine made by Hirose Iron Works (Osaka). Mitani’s printing presses were introduced between the 1950s and 1970s, and Hirose Iron Works’ large-format printing press was introduced in 1995. The large-format press has a maximum print size of 24 × 48 inches (about 600 × 1200 mm). The other presses have a maximum print size of 20 × 24 to 25 inches (approximately 500 × 600 to 635 mm). These machines are known as flatbed cylinder presses, which are equipped with impression cylinders that rotate and apply pressure against a flat plate to print.

Printing is carried out using pigment inks used in collotype printing. The inks are produced by Mitsuboshi Printing Ink (Osaka). With a pigment content of 60%, the ink is extremely hard, offering excellent lightfastness and weather resistance.
The ink is manually spread with a spatula and evenly applied across the metal plate of the press. The glass printing plate is dampened with water using a sponge. Gelatin expands when water is applied, but areas that have been exposed to light and hardened do not expand. Since oil-based pigment ink repels water, areas that received stronger exposure retain less moisture and hold more ink, while areas that received little exposure retain more moisture and hold less ink. This results in differences in shading, which enables rich gradation.

The paper is fed manually, one sheet at a time. The properties of paper naturally vary by type. But printing behavior also varies with the season and climate. When handmade washi paper is used, the thickness varies piece by piece. For this reason, before the paper is fed through the printing press, each sheet is gently rolled to remove creases and ensure uniform passage.

Benrido has produced many reproductions of national treasures and important cultural properties. However, this was their first attempt at producing prints using the vivid colors found in manga illustrations. When printing using more than 20 plates, minimizing plate misregistration wasn’t the only challenge. There was also concern over whether the washi paper could withstand this level of multi-color printing. During the printing process, each printed sheet was checked one by one with a loupe.