A couple of years ago, I started blogging about #6 plastic, and how it can be shrunk in the oven to make really neat earrings. Since I started, there are a few things I've learned about this stuff.
The lids and containers these are made from: The way those were made in the first place is by being stretched into gigantic, thin sheets. The material reacts on memory. So when you shrink it again, it wants to reverse in the same direction.
That's why I get some rectangles that come out longer, and some wider. This can make it very difficult to control. And, as in the case of earrings where I'm wanting matching pairs, somewhat frustrating. I will get a better yield if I keep adjacent pieces from the same sheets, that were cut in the same direction, together.
Safety: Shrinking this plastic without use of proper ventilation may be very harmful! Where I used to live, the exhaust on my oven was very effective at venting any fumes outside. Once, I thought using a toaster oven might provide a more even heat source or something-but the fumes had no vent! It was horrible. I had to turn on a bunch of fans and get out of the house. So please, if you must use a toaster oven, set it up outside.
Other notes: It would be fun if we could cut out other shapes, like letters, or triangles, swirls. Of course you could try that, but I've found that more corners or angles tend to curl up when they shrink. Once my brother and I cut a #6 plastic foggy-type drinking cup. A piece of the curved side. It shrunk to a white, curled up piece like a thick tortillion or a seashell.
If you need more details on this home-made shrinky dink, see this old post-I'm sorry about the missing pictures, please forgive me =(