Hector Martin

I'd had chekis taken before (Japanese term for these photos), but I only just realized that they are exposed from the *rear*. This way they don't need a mirror to get the image right side up. I took one apart and it's quite interesting. Might do another one with photos later.

Unlike Polaroid, there seems to be no chemical opacifier process. There doesn't need to be, because you see the photo from the other side anyway! The processing fluid is pitch black, and that immediately shields the exposure side as the photo is ejected, and stays there forever.

So instead what happens is there is another double barrier on the other side of the emulsion layers: a black light-shielding layer and a white light-reflective layer. As the photo develops, the dyes migrate *through* these layers. And that is what you see.

So everyone says that on Polaroid what you see as the photo "develops" is just the opacifier clearing out, but on Instax, you really *do* see the photo develop before your eyes, i.e. the dyes migrate (and in fact you can see the cyan layer make it there first).

Then there is a neutralization/timing process just to stop the (basic) processing fluid after some point, and to make the photo safe to handle/abuse (unused film is caustic inside). Those layers are on the exposure side and are just clear to the eye.

If you delayer one of these photos, you can see the rear window (clear/slightly tinted), clear gel-like acid/neutralization layers, pitch black processing fluid remnant, and then a shadow of the image from the rear side after you get rid of all the black goop.

If you keep rubbing under water, you can see that the emulsion layers hold dye in the negative pattern of the image (the parts that didn't make it through), and if you're careful you can rub down to the light-reflective layer (white) without destroying the photo.

That leaves you with a slightly translucent, rather delicate photo with a white back (it's pretty easy to scratch it from the rear). The dyes in the image-receiving layer do seem to retain a bit of layering too (cyan/magenta/yellow are not in the same exact plane).