Diazotype
The diazotype is a silverless photographic blueprint process . The diazotype was also called ozalid copy after a former brand of ozalid paper . Works made with this process are called blueprints.
The diazotype is a positive process in which the dark lines of the original on a light carrier also become dark. A polymer with azo dye is formed . It works without emulsion , the color is created in a dry process under ammonia vapors directly on the carrier.
As the carrier, paper (including tracing paper, here called master print), plastic (cellophane, cellulose acetate, polyester u. A., Called film break here) or serve textiles. The mother and film breaks had the advantage that they could be edited as originals and used for duplication. The diazo type is relatively matt, dark purple or dark brown depending on the product. Depending on the exposure and transparency of the original, the background appears white to purple or brown-gray.
Diazotypes on tracing paper can be used as an intermediate negative for further reproductions. The chemical process differs from the cyanotype , the blueprint.
history
The processes patented in the 1880s were still negative processes with wet development, which were mainly used for the textile industry. Only positive methods have been used since the 1890s. 1917 (?) Led the chemical factory Kalle & Co. AG Ozalid a -copy. It was invented by the Benedictine Father Gustav Kögel (* 1882 in Munich, † 1945 in Karlsruhe). It is based on a photosensitive paper with great stability before exposure and high photosensitivity for sharp reproductions.
The term ozalid is derived from the backward reading of the prefix diazo (diazotype, azo dye), into which an "l" was added to make it easier to pronounce.
In 1920 Kalle brought the first drying process on the market, in which the development took place through ammonia vapors. When the patents expired after the Second World War , numerous processes were developed on this basis, and since the 1940s also with the principle of development through heat.
functionality
Diazoemulsions contain light-sensitive color couplers which break down into components that are no longer capable of coupling when exposed to light. Chemically, it is a photopolymer process with a photochemical rearrangement ( Wolff rearrangement ) of 2-aminophenols to form cyclopentadiene . The light-sensitive basic substance are diazonium salts (nitrogen compounds). During development, a positive dye image is created in the unexposed areas.
The original is placed as a transparent film on so-called diazo paper and exposed with a UV lamp . The Diazo paper has a UV- sensitive surface. The diazo layer is retained in the places where there are dark places in the original that do not allow light to pass through. In all other places the layer breaks down into a colorless compound.
The exposed paper is now exposed to ammonia vapors. The remaining diazo layer reacts with the ammonia and forms a diazo dye. The exposed areas remain bright. The remaining ammonia evaporates and the copy remains dry, which is why this is also referred to as the dry pause process.
Areas of application
Diazotype was particularly suitable for reproducing technical drawings and was therefore widespread in engineering (e.g. mechanical engineering, civil engineering and architecture) until around 1990. The originals were created with Indian ink on parchment paper, later also on special foils. Mother pauses and originals on transparent / parchment paper could also be edited and changed with the razor blade, paper pauses could also be erased to a limited extent. Another advantage of the diazotype both on paper and on transparency is that it can be reproduced practically 1: 1 without shifting the scale, since the printing process does not require heat setting and the material does not shrink or expand.
The diazotype continued as proof for artwork popular and for the presentation of graphics in presentations. The process is also used in the production of printing plates (offset printing), positive photoresists and light-sensitive layers for screen printing .
Preservation
The phenols in diazotypes react with oxygen , intensified under UV light , and lead to discoloration. This effect occurs mainly on the sides that come into greater contact with oxygen. The color is sensitive to acids, which leads to self-dissolution due to the acidity of the diazotypes.
See also
literature
- Eleonore Kissel, Erin Vigneau: Architectural photoreproductions. A manual for identification and Care. Oak Knoll et al., New Castle DE et al. 1999, ISBN 1-884718-62-0 .
Web links
Individual evidence
- ^ DPMA trademark register
- ↑ Patent DE467766 : Process for the production of anaglyphs. Registered on December 2, 1927 , published on February 27, 1930 , applicant: Kalle & Co. Akt-Ges., Inventors: Gustav Kögel, Maximilian P. Schmidt, Rudolf Zahn.