Wet-plate collodion photography is a process that lets you develop a photo onto a piece of glass. It has some neat applications, but it's not a simple process, and most people use a special camera to do it because the silver nitrate used to process usually ends up leaking, which would ruin a regular camera.
Turns out, the film holder in Polaroid cameras (100-400 series) can be modified into a wet-plate holder. And, since the company has stopped making instant film, you may as well get some use out of the camera, right?
Jalo Porkkala of Alternative Photography created a tutorial that shows how to turn your Polaroid into a wet plate camera. And don't worry, if you have some leftover film for it, you'll still be able to use it after converting.
First, Jalo removed the film holder and disassembled it by pressing in on the sides and taking off the back plate, which can be thrown out.
Jalo used a piece of tape as a hinge and a steel spring to hold the plate in place during exposure. To load it, all you have to do is put a piece of glass or metal into the frame. For the long exposures required in wet-plate photography, you'll need to put a piece of black tape over the light meter eye and hold down the shutter release.
Check out Jalo's tutorial for more details on how the process works and to see example photos. He's also included guides on enlarging a wet plate photo and how to use collodion with a digital image.