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For example, the Jobo tank states that 240ml of liquid is needed for rotation development, while 485ml is required to submerge the film fully.

I've seen many people saying that the rotation method thus "saves chemicals", but this sounds odd. Shouldn't the total capacity of a batch of chemical remains the same?

Say I mixed the chemicals into 1000ml of liquid for the C41 process, I can use 240ml or pour the entire 1000ml into the tank but either way, the capacity of this batch of chemicals is reduced by one roll and one roll only.

I assume this is the case since water is not an active ingredient in the film's chemical reaction. And that it makes no sense for CineStill or Flic Film to say their chemistry can process certain rolls of film if the volume of liquid matters. But this would also mean 240ml and 485ml makes little to no difference in terms of chemical usage.

Exactly what is the relationship between liquid volume and chemical usage? Or is there some hidden variable that I did not take into consideration?

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  • \$\begingroup\$ Re, "relationship between liquid volume and chemical usage." It's going to be, between liquid volume and film area and chemical usage. I'm going to further guess that film area is more important than liquid volume. IDK for sure though: When I developed my own films (strictly B&W) I always filled the tank. \$\endgroup\$ Apr 25, 2023 at 1:04
  • \$\begingroup\$ @SolomonSlow right. Certain are of film consumes a certain amount of effective chemical component in the liquid. One could supply more liquid solution than this area needs but the amount of effective chemicals used in the reaction will not increase, since the reaction stops after that area is developed (not considering push or pull). That's what I assumed \$\endgroup\$ Apr 25, 2023 at 13:41

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Another way to look at it comes from Kodak's data sheet on Xtol developer. It states that one roll (35 mm x 36 or 120 roll) is 80 sq. inches and requires 100 ml of stock developer regardless of the dilution when used. Diluting developer to increase volume to completely cover the film will require longer developing time because of the lower concentration of active chemicals.

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Developers

  1. Water solvent
  2. Developing agent black & white (likely two)
  3. Color developer
  4. Accelerator (alkaline to set the pH)
  5. Restrainer (bromine)
  6. Preservative (oxygen dissolved in the waters of the developer attacks the developing agents. Spent developer reduces activity and the byproduct is coal tar. Developers are derivatives of benzene initially extracted from coal. The preservative retards staining.

As development runs its course, the black & white developers seek exposed silver salt crystals. These developers reduce the silver salt to metallic silver and halogen. Halogen is Swedish for salt maker. There are three in common use, silver bromine, silver chlorine and silver iodine.

The developer solution contains bromine which controls the rate of development and reduces the likelihood that the developing agent will act on unexposed silver salts. Bromine (restrainer) is one of the key ingredients. As development continues silver salt crystals are reduced to their two component parts i.e. metallic silver and a halogen (bromine). Thus, the concentration of the restrainer increases, and this reduces the activity of the developer. Additionally, the developing agents are being exhausted.

In a continuous film developing machine, a developing formula called a replenisher is metered into the developing tank. This fluid is void of bromine, however the solution gains bromine from the developing silver salts. The developer replenisher solution restores the developer allowing it to have an indefinite life. In a non-replenished system, the developing agents are being oxidized and thus exhausted, the pH is being altered and staining agents are increasing.

The black & white developers generate a metallic silver negative image. The film additionally contains incomplete cyan, magenta, and yellow dyes. These are missing a single ingredient. Without it they are colorless (in a leuco state Latin for white).

As the metallic silver is formed, dissolved oxygen in the waters of the developer attacks and it is tarnished. This action is the catalyst that causes the color developer to give up the missing dye ingredient to the globules of leuco dye adjacent to the metallic silver tufts. The dyes this blossom forming a color image. Now we have three negative silver images, three dye images. In regions not exposed, two of the leuco dyes have a warm tint. This yields the orange coloration which is actually two positive images superimposed atop the three negative color images. This is called masking. The mask bolsters the cyan and magenta dyes. This is needed because they are not quite the right shades.

The bleach step attacks the metallic silver image. The bleach converts the silver back to a silver salt. The fixer in the bleach or in a separate step is a solvent for silver salts. The colors are now unveiled.

The stabilizer is a biocide and rinse agent. The dyes are organic and subject to become food for beasties. The biocide protects.

It is the total volume of the unreplenished solutions that determines the amount of film that can be processed.

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