We do not currently have a published data sheet regarding reciprocity failure compensation. There is not a consistent method for calculating reciprocity characteristics for color negative film, as color negative film is made up of multiple halides and dye couplers on three separate emulsion layers, each of which react differently to low intensity exposure. In fact, most color films do not have published reciprocity failure compensation for exposure times longer than 1 second, since the resulting color layers could have varying densities based on the different wavelengths in the exposure.
Contrast is also increased with long exposures and can result in further color shifts. This is because of the intensity difference in exposure between highlights and shadows in the image, in effect giving different reciprocity failure within each color layer.
Some B&W emulsions have published data that can help film photographers achieve reciprocity failure correction with a single emulsion. As indicated above, this differs from emulsion to emulsion, but a general guide involves increasing your exposure time by a factor of 1.3.
Corrected exposure time ≈ metered exposure time to the power of ^ 1.3
Tip: the “Xʸ” button can be found on most smart phone calculators when used in landscape mode.
When shooting CineStill films in low light with metered exposure times over 1 second, you can try applying the above guideline. It’s also a good idea to bracket your exposures by a couple stops. For very long exposures in very low light some other variables come in to play such as the accuracy of the light measurement. This means that some trial and error may be required. As with all color negative film, it’s usually best to err on the side of giving the film more exposure to create a denser negative with more information for color correcting when scanning or printing in the darkroom.