These pieces come from an empty bottle of port. I cut it in half with a knife, then smoothed and evened out the edges with a pair of scissors. After that, I kid you not, you rub the raw edge against a hot iron. The plastic does NOT melt and stick to the iron- go figure.
The heat from the iron smooths the raw edge and also melts it inward so it forms a formal looking lip on the plastic.
I used the top half of the bottle, cap still in place, to make a bird feeder:
After a treatment on the hot iron the bottom half of the bottle became a pencil holder, or glue holder for my scrapbooking empire.