Rodinal

Rodinal is the trade name of a black and white developing agent produced originally by the German company Agfa based on the chemical 4-aminophenol.

Rodinal was patented January 27, 1891 by Dr. Momme Andresen. It was the first product sold by Agfa and is the oldest photographic product still available (2014). After the patent expired, Rodinal has been supplied under different names by other companies. Rodinal is a concentrated liquid developer with very long storage life; the working developer is used once. This may have helped sales to amateur users who did not have to make up an entire packet of developer, enough for many films but with a short life once made up.

Rodinal has for a long time been manufactured in a chemical plant in Vaihingen-Enz owned originally by Agfa. In November 2005 the plant was sold to a&o Imaging Solutions GmbH in Koblenz, Germany, who continued the production of Rodinal. In 2008 it was sold again to Connect Chemicals (Ratingen, Germany.) Today Rodinal can be obtained from ADOX Fotowerke Bad Saarow, Germany. It is now called ADONAL.

Rodinal is sold as a long-lasting concentrated liquid which is diluted with water for use, typically at 1+25, 1+50 or 1+100. Higher dilutions than 1+100 will slow down development and increase the perceived sharpness of the film. Working solutions can only be used once and will not keep even if unused. Stand development of sheet films, oriented vertically with high dilution, no agitation, and extremely long developing times can be used for special purposes. The most complete listing of Rodinal development times with a wide variety of films may be found at the Massive Dev Chart or the Comprehensive Development Times Chart.

Rodinal increases perceived edge sharpness dramatically: in the case of standing development ( no agitation for long developing time, an hour or more) the developer is used up more quickly in dark than in light areas, development of light areas next to dark areas (the edges of the image) is reduced, increasing contrast at edges. Very dilute Rodinal (1 part to 100 or more) is often used to maximise this effect.

Rodinal is not a fine-grain developer, and is best used with film of low and medium sensitivity, with inherently finer grain than high-speed films, or with larger film sizes.

A well-known property of Rodinal is its high acutance, because the Rodinal formula contains no silver solvent. Consequently the metallic silver in film, once developed, is left in its natural state, and does not undergo any "softening" by means of a solvent. It is not uncommon for photographers to add a solvent (such as sodium sulfite) to soften the granularity.

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