What causes photos from modern instant films cameras to look unique?

Question

I just saw a picture from a friends Polaroid Instant Camera or Fujifilm Instax, and even when it is freshly developed (no aging or anything) the pictures have a distinctive "look", like a sepia effect with color, with the slightly off white balance. I was wondering, what causes the specific look both in the chemistry of the film, construction of the camera, and the optics?

Here is an example by Mrnerd1billion made by Ryan Notch of www.areographers.com - Own work, CC BY 3.0

I know that the low element lens might cause aberrations that cause the pictures to look nostalgic, but what are the technical differences in the instant films cameras that cause the pictures to look different from a standard disposable film camera or even SLR film camera?

Answer 1

What causes the pictures produced by any chemical process to look unique?

The specific chemistry involved. Different chemical processes are more or less responsive to various wavelengths of light. One film emulsion might be more responsive to the red end of the spectrum, another might be more responsive to blue. Another might be highly responsive to green and less responsive to both red and blue. This is true not only of "instant" film, but also of more traditional negative film and positive reversal films that require development with chemicals not included in the film's emulsion.

It's the reason there were near endless arguments about whether Kodachrome, Portra, or Velvia was "better" for a specific use case, or whether Kodak VR Gold 200 or Fuji HQ 200 gave more "bang for the buck".

Additionally, with most "instant" film there is a mechanical process involved which forces the light sensitive chemicals in one layer of the emulsion to mix with the dye couplers and developers in another layer. The physical pressure used to do this tends to spread the exposed light sensitive chemicals a bit, which, on a microscopic level, spreads the exposed chemicals out. This blurs the image a bit, again on a microscopic level, but also smooths the gaps between grains of different colors.