system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How do polaroid pictures work?

How do the pictures just slowly come in there etc?
gpt
Freakin' magic, that's how!

In a nutshell, a polaroid is a little envelope that contains all the chemicals needed to develop and fix the picture.  Light hits chemicals that are sensitive to light, which react with reagents in a different layer that cause dyes to migrate into the first layer and become visible.

Developing a photograph takes time (the chemical reactions aren't instantaneous), and the first process to do instant color prints didn't work very well.  The solution was to add another layer of chemicals that opacify soon after the exposure to light.  This makes it dark inside the layers, and allows the time necessary for the developing and fixing process to happen without being exposed to more light.  That opacifier breaks down and becomes clear after a period of time.   That's what you're actually seeing when the polaroid comes out grey and image slowly shows up.