Rodinal

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

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History

Rodinal was patented January 27, 1891 by Dr. Momme Andresen. The main selling point of Rodinal was its availability as a liquid developer rather than in powder form, which eased the process of making up developer for film development. Rodinal was the first product ever sold by Agfa and is the oldest commercially available photographic product that is still being sold today (2007). After the patent expired, Rodinal started to be sold under different names by other companies.

How to use

Rodinal is sold as a concentrated liquid and has to be diluted. 1+25, 1+50 and 1+100 are common dilutions, wherein 1 part Rodinal is diluted to X parts water. Higher dilutions than 1+100 will slow down subsequent development and increase the perceived sharpness of the film. Working solutions can only be used once.

• See also: film development.

Edge sharpness

Rodinal is known for increasing the perceived grain of many black and white films. However, it also increases edge sharpness dramatically: since 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. This increases the contrast at the edges and therefore also increases the perceived edge sharpness. Rodinal is often used in very high dilutions (1+100 and above) in order to maximise this effect.

High Acutance

A well-known property of Rodinal is its high acutance, due to the fact that the Rodinal formula contains no silver solvent. As such, 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.

References