During Design Week Kyoto, I participated in a workshop at Benrido. Benrido Collotype Atelier is one of four printing workshops worldwide that has preserved collotype and perfected it with modern technology. Collotype was invented in France around 150 years ago and was primarily used for printing photographs and illustrations. Today, only a few use this method, since it is very complex and expensive and requires a lot of craftsmanship and experience. By means of collotype, one can print halftones (mixed colours) without a dot matrix system (in contrast to the offset printing, for example, where one recognizes the individual colour dots within a colour surface), which produces a high quality. Since you can also print on a variety of materials, such as linen, rice paper or vellum, this technique is now mainly used as an art form and in making facsimile (replica of works of art).
How do you create collotypes?
Since collotype was invented in 1856, the technology has developed steadily in proportion to photography. If you were initially only able to print black-and-white images, today you can print up to 20 plates on top of each other for specific shades. For this, the colours have to be decomposed, for which Benrido photographs the original with four filters (red, green, blue and yellow). Technicians then check the colour decomposition against a colour composite swatch book. For a few years, digital aids can be used for this, which makes the result even more precise and the process even more efficient.
For the printing process, every single colour to be printed requires a single colour (black) negative. The technicians check every single negative and, if necessary, adjust in case they notice inconsistencies compared to the original. For this purpose, defective areas are covered with masking film.
Production of printing plates
The base is a 10mm thick glass plate coated with a light-sensitive emulsion of dichromated gelatin. This is clamped in the exposure table and the negative placed on it to expose both together with UV light. Due to the darker areas of the negative, less or no UV rays penetrate. Where the light strikes the coating, the chromate salts contained in the gelatin harden the gelatin. The result is a relief, which is more pronounced, the more light penetrates. Then immerse the plate in cool water to wash out the chromates, which prevents further exposure.
To prepare the plate for printing, it is moistened with a solution of 50% water and 50% glycerine. The stronger the gelatin relief, the less water the surface can absorb.
The collotype ink is composed of 60% pigments and 40% oil. Now when it is applied to the moistened plate with a roller, the areas that have absorbed the liquid repel the paint. It sticks to the roller. The less liquid absorbed, the more ink will adhere to the surface of the plate. The areas that had the least UV light, and thus soaked up the most liquid will be the brightest spots in the final print; whereas the darkest areas previously were exposed the most and thus absorbed the least liquid. Consequently, a full continuous tone image is formed.
During printing, the paper is hand-fed into the printer one sheet at a time.
When all the sheets of one colour have been completely printed, the plate is replaced with the one of the next colour. One plate can be used for 1000-2000 prints. The individual colours are printed on one another in layers and then reassembled. All ink colours are made of special mixtures of different pigments. In order to be able to print colour layers well on each other, you must first analyze the composition accurately.
Benrido offers various workshops. As part of Design Week Kyoto, I participated in a small workshop in which I was able to print two postcards with a collotype.