That's basically how Polaroid pictures work(ed). The developer/fixer was in the bottom edge, and this container was punctured and the chemicals squeezed out by

That's basically how Polaroid pictures work(ed). The developer/fixer was in the bottom edge, and this container was punctured and the chemicals squeezed out by the rollers as it came out. The only thing left would be to distribute it along the back of the photograph, so you, you know, shake it.