Whiteprint

The diazo process is a silver -free photographic Lichtpausverfahren. According to a former brand of paper Ozalid the diazo was also called Ozalidkopie.

The diazo process is a positive process, also be dark in the dark lines of the template on a light carrier. It forms a polymer with azo dye. It is carried out without the emulsion, the coloring produced in a dry process with ammonia vapors directly to the substrate.

As carriers, paper (including tracing paper, here called Mother pause), plastic ( cellophane, cellulose acetate, polyester and Others, here called film break ) or textiles serve. The mother or film breaks had the advantage that they could be re- edited as an original and used for reproduction. The diazo process is finished, the ground is dirty stained white, the unexposed areas can take depending on the product, different colors, most common are purple, blue, black or brown.

Diazotypien on tracing paper can be used as an intermediate negative for additional copies. The chemical process is different from the bluing also cyanotype with which the blueprint is often confused.

History

The patented in the 1880s, cases were still negative process with wet processing, which are mainly found use for the textile industry. Since the 1890s, positive methods are only applied. 1917 led the Chemische Fabrik Kalle & Co. AG Ozalid the copy. It was in 1917 by the Benedictine Father Gustav Koegel (* 1882 in Munich, † 1945 in Karlsruhe) patented. It is based on a photosensitive paper with great stability before exposure and high sensitivity for sharp reproductions. The term Ozalid is derived from the backward read prefix diazo ( diazo, azo dye ), in which one then another "l" einfügte to better enunciate. 1920 brought Kalle the first drying process on the market, in which the development was carried out by ammonia vapors. When, after the Second World War, expired patents, numerous methods developed on this basis, since the 1940s with the principle of development by heat.

Operation

Diazoemulsionen contain light-sensitive color couplers, which decompose upon exposure to no longer capable of coupling components. Chemically, it is a photopolymer process, with a photochemical rearrangement ( Wolff rearrangement) of 2 -aminophenols to cyclopentadiene. The photosensitive diazonium salt is ground substance ( a nitrogen compound ). Arises in the development of the unexposed areas, a positive dye image.

The original is set as a transparent film on a so-called diazo paper, and exposed to a UV lamp. The diazo paper is provided with a UV - light -sensitive surface. At the places where dark spots are present in the original, which can happen no light, the diazo layer remains. At all other places, the layer breaks up into a colorless compound.

The exposed paper is then exposed to ammonia vapors. The still existing diazo layer reacts with the ammonia and forms a diazo dye. Exposed points remain bright The residual ammonia evaporates and the copy remains dry, so you can also talk about Trockenpausverfahren.

Areas of application

Diazotype was particularly suitable for reproductions of technical drawings and therefore in the engineering sciences (eg Mechanical Engineering, Civil Engineering and Architecture ) widespread until about 1990. The originals were later created with ink on parchment paper, both in specific films. Master prints and originals on Transparent-/Pergamentpapier could also be edited with a razor blade and changed, paper breaks could be caused also erasing. Another advantage of the diazo process is both paper and on transparent that the reproduction virtually 1:1 without displacement of the scale is possible because the printing process requires no heat-setting and ensure that the material does not shrink or expand.

The diazo was still popular as a proof for artwork and for the presentation of graphics for presentations, because the blue color looks more pleasant than black and white reproductions. In the manufacture of printing plates (offset printing), positive photoresists, photosensitive layers for the screen printing method is applied.

Preservation

The phenols in Diazotypien react with oxygen, enhanced under UV light, and cause discoloration. This effect occurs especially at the sides which come into contact with more oxygen. The color is sensitive to acid, which leads to self-destruction because of the acidity of the Diazotypien.

Use as a figure of speech

Frequently "blueprint " in the context of business management, economics and politics is used. Metaphorically, which is actually purely technological meant word blueprint for an authoritative master form or a master plan, for example: " The politician looks at the successful outcome of the meeting drawn up a blueprint for working together in the coming years. " Such a master model is copied in the sense of a blueprint or transferred to other processes or areas. Thus often unique developed models serve as a blueprint for a variety of business strategies.