The trick to those double edged, or triple edged pictures? It's simple, click your shutter more than once! All you need is a little thought put into your photos, just a little.
The first time that I had seen a multiple exposure photo, I was totally baffled. Do you take the lighter picture first? Or the dark one? How can it all be in one photo? And why??
Well, the basics of a photo with more than one exposure is easy: the darker parts of the first photo will be exposed to the second picture that you take. This was my first mx photo:
I happened to take a self portrait. Since I have lots of black hair, that part of the negative is less exposed so the second photo (flowers) filled in my hair and some parts of the background.
If you have slow film, your film will be darker and you will be able to take triples or quadruple exposures. With slow film or dark places, you won’t have to think about where the dark parts of your photo will be.
To put it as simply as possible, the portions of negatives that aren’t darkened will be filled in when you expose the negative twice. So if you have a photo like this:
the black part would’ve been filled in with another photo if I’d taken the second shot.
So you see, multiple exposures are really simple, click twice or thrice and you can make your own masterpiece. Have fun with it :)