Collotype (pressure)

from Wikipedia, the free encyclopedia
Early picture postcard with collotype of a photo from the First Bavarian State Exhibition;
1882 in Nuremberg , signed J. B. Obernetter

Collotype (also known as phototype, collotype, albertotype) is a rare printing process .

In a broader sense, it refers to all photomechanical ( photolithographic ) flat printing processes for reproducing halftones without a grid , but in a narrower sense only the process developed by Louis-Alphonse Poitevin in 1856 under the name of collotype and improved by Joseph Albert in 1870 , with which larger editions can be made made. Karl Klietsch developed the heliogravure from this in 1879 .

use

Collotype, scan from original 1865, Chartres Cathedral
Collotype postcard around 1900

Collotype printing was widespread around 1900, but was superseded by offset printing in the 20th century . After the closure of the Dresden collotype workshop , four collotype printers still exist worldwide: in the Museum für Druckkunst Leipzig , in the world's oldest photo workshop of the Alinari brothers in Florence , at Benrido-Druck in Kyoto , Japan and the Offizin workshop in Darmstadt .

In addition to color lithography , it was primarily used to illustrate books or prints in small editions such as viewing, memorial or postcards. Initially, no processes were known that reproduced drawings, paintings or photographs in a comparable quality.

Artists have used collotype for graphics for independent statements. One example is Willi Baumeister with his twenty original collotype prints, which were published by the Flechtheim Gallery in 1929 in a portfolio of 200 copies, Sport und Maschinen .

After the spread of the process gradually declined in the middle of the 20th century, it is still used outside the immediate artistic field for the facsimile of works of art such as paintings, medieval manuscripts and documents. The playback quality is unmatched for this.

With its means and possibilities, collotype represents its own art form. In Leipzig, collotype printers and visual artists such as Olaf Wegewitz worked together to develop techniques and processes for artistic design on the printing plate. Thus the collotype original graphics became a form of graphic art. The tried and tested possibility of exposure to various semi-permeable and permeable materials on the printing plate has created a new way of expressing itself in photographic work. These two versions are recognized as separate art forms.

Printing form production

Detail from the above postcard
with clearly recognizable wrinkles

The carrier of the printing form is a ten millimeter thick, matt etched, very flat glass plate (mirror glass without a mirror layer) or a metal plate. A light-sensitive emulsion made of chromate gelatine is applied to the plate in two layers (pre-layer and printing layer) and dried in the semi-darkness. The emulsion consists of gelatin which has been made photosensitive with ammonium dichromate or potassium dichromate .

A photographic halftone negative is then exposed onto the plate using light with a high UV component . In contrast to most printing processes, the negative is not screened. When exposed to light, the chromate salts contained in the gelatin change the solubility of the gelatin in water and convert the negative image into a gelatin relief . This process is called tanning of the gelatin. The amount of light that hits it determines the height of the “tanned” gelatine. The peculiarity of this copy layer lies in its ratio of the amount of light to the degree of curing:

  • little light = little hardening
  • a lot of light = strong hardening

After the copying process, the plate is immersed in five to ten degrees cold water, which washes out the chromates and prevents further exposure. The characteristic wrinkled grain is formed , on which finished collotype prints can be unmistakably identified when magnified.

If a multicolored result is desired, corresponding printing plates are made for each printing color. For facsimile prints of works of art, up to 20 plates for certain color tones are sometimes printed on top of one another. This makes it possible to achieve prints that are very faithful to the original.

pressure

Before printing, the printing plates are usually moistened with a glycerin-water mixture. The swelling of the gelatine, depending on the degree of hardening - and therefore depending on the degree of exposure - determines the tonal value to be reproduced. There is a relationship between exposure and the uptake of ink at the relevant point. The following applies:

  • low hardening = strong swelling, little printing ink
  • strong hardening = slight swelling, a lot of printing ink

The water that is more abundant in swelling areas plays a role here: it repels the greasy printing ink, whereas the more hardened areas accept it. In the collotype flat-form cylinder press , printing takes place in this printing process. These collotype high -speed presses are constructed in a similar way to the offset single-color flat printing presses . Converted lithographic machines were often used. The daily number is between 600 and 1000 sheets and requires a high level of professional experience and concentration on the part of the printer. The fine "source relief" can be controlled in contrast by further moistening the printing form. Stronger moistening decreases, weaker moistening increases the contrast.

The appearance of the print can be influenced by chemicals that are applied to the printing gelatin layer. Formalin fixes the gelatine, alum makes individual printed parts darker because it has a hardening effect. Potassium cyanide is hygroscopic, it attracts water, makes the gelatine softer and so individual printed parts become lighter.

The relative humidity in the vicinity of the print must be kept constant at all times. In this respect, the production run must be constantly monitored. The printed sheet is inserted into the printing machine by a helper and the printer takes it out of the machine and assesses it after the printing process. The print run can reach 1000 to 2000 prints, after which a new printing form must be created. The gelatin layer is stressed by the printing processes and damaged in the process.

The editions achieved are low and the workload in collotype is very high. Collotype is expensive, but the reproduction quality justifies the high price. In the early days, collotype printing was comparable to other printing processes in terms of the amount of work involved and the printing result produced a printed product that could not be achieved in any other way.

A special feature of collotype is the oil-based, but particularly strong and tough collotype ink. Processing is only possible with special, strong color rubbing knives . Before each use, it is under immediate addition of oil varnish again with this color meter (printer Patel) durchzuwalken so that the paint is ready for use.

Collotype prints, if they are stored in book form in a relatively airtight manner, can emit a stronger odor from the chemicals used, for example of ox bile, which is used during printing to avoid annoying, co-printing edge tones.

literature

Web links

Individual evidence

  1. ^ Museum für Druckkunst Leipzig: Collotype Art Leipzig ( Memento from July 16, 2015 in the Internet Archive )
  2. ^ Fratelli Alinari: The Collotype ( Memento from February 13, 2012 in the Internet Archive )
  3. ↑ Benrido Printing Co., Ltd. Kyoto: コ ロ タ イ プ 印刷 ( collotype )
  4. ^ Offizin Darmstadt