LITH DEVELOPERS

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This information was taken directly from an e-mail from Michael Gudzinowicz (bg174@FreeNet.Carleton.CA). It is the best description so far on what Lith Developers do.

Lith Developers are fairly simple mixtures. Hydroquinone is the developing agent, usually present in a concentration of around 20 grams per litre. The free sulphite level must be very low - less than 2 grams per litre. Since the developer will oxidise quickly, sulphite in the form of an addition product with formaldehyde is frequently used, or formaldehyde, paraformaldehyde or acetone are added to tie up free sulphite. The anti-oxidant properties are retained. The third component is a base, usually carbonate or mixtures of carbonate, hydroxide or borates. The pH is frequently adjusted to a value around 10.

Although lith developers are often thought of as simply high contrast developers, they have a unique property. In the absence of sulphite, the hydroquinone dianon reduces silver and is oxidised to the semiqinone free radical. The semiquinone is a more powerful developing agent than hydroquinone, and it reduces another silver atom and is converted to quinone. Then quinone reacts with hydroquinone to form two semiquinone molecules. They reduce silver, generating two quinones. They react with hydroquinone forming four semiquinone molecules. The rounds of reactions result in an exponential inrease in semiquinone concentration, doubling each time. The addition of sulphite will stop these reactions, since it reacts with the semiquinone and quinone removing the possibility of reaction with hydroquinone to generate more semiquinone.

The semiquinone is generated in the emulsion and remains there with a very short diffusion path. Development starts with grains which have multiple centres. The semiquinone concentration rises as those grains are reduced, and then neighbouring grains are developed which might have just one centre. As the concentration rises a bit more, development spreads explosively (exponential).

What one sees is that development starts slowly in well exposed areas of the film. If a step tablet were used for the exposure, a faint image appears in the well exposed areas. Eventually the developed area reaches a critical density and semiquinone concentration, and then development takes off, and quickly goes to completion in that step. Then as development proceeds, the next step develops fully.

Essentially one has a two phase development. First the formation of a faint image, then rapid completion in areas receiving the most exposure. This results in a film with very little density in areas with little exposure, and an extremely dense image in areas with a bit more exposure. As expected, the contrast increases with development to a miximum after 1 to 3 minutes, and then decreases as the low value faint images are further developed. Unlike developers with moderate sulphite concentrations, development is restricted to the grain and filaments are not formed. If free sulphite is added (20gm/l), filaments are formed and neighbouring grains are rapidly developed. There is no lag phase and significant semiquinone concentrations are not generated. The developer then acts like a typical MQ or PQ high contrast developer.

Having read the material from Richard and Michael about lith developers, I then consulted my copy of Wall "Photographic Facts and Formulas" (reference on my Library Page) and discovered, in addition to two formulae, a note that Hydroquinone deteriorates slowly in air and has good keeping qualities in solution but is very sensitive to cold and should not be used at temperatures below 60 degrees F. It is practically inert at 55 degrees F. I then went to The Focal Encyclopedia of Photography (Desk edition), Focal Press, London, 1969 and discovered a table comparing lith developers. I've modified it slightly and reproduce the modification here. It gives a different version of Kodak D-8 which is a bit inexplicable.

Most lith developers only have a working life of 2 hours or so.

ACETONITRILE ANTIOXIDANT DEVELOPER

AGFA / ANSCO / GAF 79 Single solution lith film developer

AGFA / ANSCO / GAF 79b Two solution version with better shelf life

DUPONT 7 D Lith film and paper developer

KODAK D 8 Formaldehyde free lith developer

EASTMAN D 9 Hydroquinone Caustic developer

ILFORD ID 13 Line screen developer

KODAK D 85 Single solution developer

KODAK D 85b Two solution developer with good shelf life

LITH DEVELOPER 1

DR JEKYLL No 1 Formaldehyde free lith paper developer