Quote Originally Posted by AgX View Post
That was what I tried to hint at. I assume gelatine gets anistropic at/towards the tiny interface with another medium.
In the context of holography there has been some research on polarization issues related to gelatin. Under certain
circumstances one might get fairly large differences between p and s-polarization.
Having said that, refractive index remains the key parameter regarding internal reflections. The degree of internal reflection may also depend on wavelength...

The reason for this I only can speculate on. It could be mechanical tension. Though I expect this would not be established in case of wet/wet coating of similar gelatine solutions.

Maybe processing (development-fixing) involves significant refractive index changes. Has there ever been research on this subject?

However, even in this case there would be an interface. In the form of a layer of wetting substances.

I guess the wetting substances (being essentially hydrophilic) would get fully absorbed by the gelatin-water layer to be coated on top of it.