By Ed Buffaloe
Rodinal is Agfa’s trademark name for their concentrated film developer formula, patented by Dr. Momme Andresen in 1891. It is the oldest continuously-produced developer formula in the world. Within twenty years of its invention Rodinal was so widely used for both film and paper that it merited its own listing in Bernard Jones’ Encyclopedia of Photography, and for a time it became a generic term for any formula that used p-aminophenol. Rodinal has a very well-deserved reputation for brilliance, gradation, and sharpness.
A number of “rodinal” formulas have been published over the years. Agfa’s has always been proprietary, but is so cheap and reliable that photographers have rarely mixed “rodinal” themselves (though Photographer’s Formulary now sells a version). Essential ingredients are the developing agent paraminophenol hydrochloride, the preservative potassium metabisulfite, and the alakali (or accelerator) sodium hydroxide. The usual formula is 3 parts potassium metabisulfite to 1 part paraminophenol, dissolved in 10 parts hot distilled water, to which is added, drop by drop, only enough of a saturated solution of sodium hydroxide to clear the precipitate which forms. [Please see the darkroom safety cautions in Mixing Developers, and handle sodium hydroxide (caustic soda) with great care.] Dilutions for this version are in the range 1:20-25. Once diluted with water, Rodinal does not keep.
Paraminophenol is a developing agent with unique properties: it produces little fog and no stain even at high temperatures, is relatively fast-working, is less temperature-dependent than other agents, can be mixed and stored in very high concentrations, and retains developing potential even at very high dilutions. The potassium metabisulfite preservative is at a low enough concentration that it has no solvent action on film grain. In high concentrations, sodium sulfite (the most-used preservative in photographic formulas) is said to literally eat away the sharp edges of silver grains in the developing emulsion. The dissolved silver is then available to be plated back onto developed silver grains in a process known as physical development. Physical development tends to blur the sharp edges of silver grains in the emulsion, reducing perceived sharpness. Rodinal avoids this drawback.
Rodinal is not a “fine-grain” developer. When miniature cameras first appeared, Rodinal fell out of favor because the early 35mm films were very coarse-grained, and looked it when developed in Rodinal. But Rodinal regained its popularity as the grain structure in modern emulsions became finer and more consistent. Conventional wisdom has it that, with Rodinal, whatever grain structure is inherent in a film’s emulsion will be retained in the developed negative. Rodinal negatives may sometimes look more “grainy” than negatives developed in the so-called fine-grain formulas, but they also have greater perceived sharpness.
Patrick Gainer has written to me to express some doubts about the role of sulfite as a solvent in developers. First of all, he states that Rodinal does contain sulfite. “Rodinal has Potassium Hydroxide, which combines with the Potassium Bisulfite to form Potassium Sulfite. Steve Anchell's 'Rodinal-type Developer' starts with 300 grams of Potassium Metabisulfite and will wind up with about 340 grams of Potassium Sulfite per liter of stock solution (if you use Potassium Hydroxide). That gives you about 14 grams of Potassium Sulfite in a liter of 25:1 working solution, which provides about as many sulfite ions as 10 grams of Sodium Sulfite. That is not enough to be suspected of eating away edges of grains, which I don't think sulfite does very much of anyway, but it is probably enough to slow down grain spreading through infectious development.”
He continues: “I am doing some experiments with D-76 to try to separate out fact from fiction. I have varied the sulfite concentration while keeping everything else the same, and I have kept the sulfite constant while changing the dilution of the rest. The results are interesting. There's no noticeable difference in graininess in 30 power enlargements between 25 and 100 grams/liter of sodium sulfite. Go figure. I know that infectious development is very important to process photography of line art. It requires minimum sulfite, which is why all those developers are kept in two parts. I believe that Rodinal has some of the characteristics of a process developer and that its grain is not necessarily the 'full, unetched grain' that is often declared, but the result of grain growth through this infectious development. In a manner of speaking, all development is infectious. It begins with an invisible latent image in only a molecule or two in a crystal and spreads to the rest of the crystal. Sulfite inhibits this growth. It appears that ascorbates also do so.”
A lot of photographers add sulfite to Rodinal to reduce the grain--a practice I always thought defeated the purpose of using Rodinal to begin with. Patrick Gainer writes: “It turns out that 4 g/l sodium ascorbate does a lot of good added to 1:50 Rodinal. A lot better than 100 g/l of sulfite.” Those who are searching for a fine-grain version of Rodinal should give this a try. (Please note: you should add sodium ascorbate, not ascorbic acid, because ascorbic acid will radically reduce the alkalinity of the Rodinal solution. Ascorbic acid is easily converted to sodium ascorbate by the addition of baking soda (in the ratio of the molecular weight of the acid over the bicarbinate, which is 176/84--approximately 2 parts acid to 1 part bicarbonate) or sodium hydroxide (in the ratio of the molecular weight of the acid to the hydroxide, which is 176/40, or 4 parts acid to 1.1 parts sodium hydroxide) . If you use the baking soda, add it to the ascorbic acid in a little water and let the fizzing subside before adding it to the working solution.)
Because Rodinal works at high dilutions, it can have a pronounced compensating effect. Compensation occurs when bromide is released in areas of heavy exposure, where development is rapid and continuous. Bromide slows the development of the high values (zone VII and above), preventing them from becoming too dense to print. High dilutions also enhance adjacency effects, which are produced when areas of high density adjoin areas of low density. Unused developer from low density areas diffuses over to the edge of high density areas and increases density even more, while bromide released by intense development in high density areas difuses over and helps prevent development on the edge of low density areas. Adjacency effects markedly enhance perceived sharpness.
Bob Schwalberg, who once wrote for Popular Photography, maintained that too much agitation would interfere with adjacency effects, and recommended no more than ten seconds per minute of gentle agitation with Rodinal. This has been my practice for years. However, Dr. Richard Henry, in Controls in Black and White Photography, states that his tests show adjacency effects are caused by “lateral diffusion in the emulsion layer” and are not dependent on agitation. In any case, Rodinal’s adjacency effects are well-documented and contribute to its reputation for sharpness.
Typically the compensating effect is seen at dilutions from 1:50 to 1:100, and can be adjusted to fit any contrast
range. I have even heard of dilutions as high as 1:200 for certain applications. Agfa recommends using at least 10
milliliters of concentrate per roll of film, no matter what dilution you use. My practice has always been to use 5
milliliters in 500 milliliters of water for the 1:100 dilution, which may account for the lengthy developing times with
some films, but it works just fine. Higher dilutions may cause speed loss, so be prepared to rate your film at about
half its normal speed. But speed loss is more than made up for by the superior sharpness and gradation Rodinal produces with most contemporary films.