Reciprocity failure...

[Vlad Soare]

Film is a chemical entity. It behaves according to natural laws.

The "Law of Reciprocity" is our attempt to describe the interaction of light with film.

To the extent that the observed interaction is not as expected, the failure lies with the law, for failing to properly describe the events under the given circumstances.

- Leigh

Film is not just a simple chemical entity. It's a combination of many chemical entities, which are carefully chosen and mixed so that they behave in a certain manner. The law of reciprocity doesn't describe the natural behaviour of each chemical entity, but the behaviour of the mixture, which is specifically and intentionally set by the manufacturer (as far as possible, of course).
What you're saying applies to plain silver halide emulsions, or to wet plates, whose photographic behaviour is set by natural laws. Modern films, on the other hand, are carefully designed to help photographers by fulfilling certain criteria, one of which is the reciprocity law.

The reciprocity law is not simply a description of a natural phenomenon, but rather a condition which film manufacturers struggle to make their films compliant with.

Fuji Across is proof that it is possible to comply with the reciprocity law to a much greater extent than most other films do. So, I'd say that the other films fail, because they don't comply with the law as closely as they could.

[Leigh]

Film is not just a simple chemical entity.
The law of reciprocity doesn't describe the natural behaviour of each chemical entity...

I did not use the word 'simple' at any time.

I did not say that the law of reciprocity applied to each chemical entity. I said it applied to the film.

- Leigh

[Jim Noel]

Shouldn't that be Reciprocity Effect ?

'Failure' is so judgmental...

ABSOLUTELY!
The film does not fail, it just records light differently when exposed for too long, or too short a time span.

[megapickle1]

Hello! I´m very interested in this problem but because I´m not a native (English) speaker I need the help from someone who is german speaking (writing). Is there anyone?
George