My wife likes to go to garage sales, and she brought home a couple of floating candle holders without the floating things that hold the wicks. I tried making some floating wick holders out of a wine bottle cork, but that turned out to be a mess that really didn't work well at all. I was cleaning up the mess I had made with the cork experiment when I noticed that the bottom of the plastic bottle I was drinking tea from would make a great wick holding floating thing. Once you have a wick holding floating thing, you can turn just about any medium to large size glass or bottle into a beautiful floating wick candle, and the cost is negligible - I was going to toss the bottle into the recycle trash can anyway.
You will need the following to make a floating wick candle:
An empty plastic drink bottle. (The kind of bottle with the five humps on the bottom. Floating wick holder things made from small drinking water bottles without the humps on the bottom tend to tip, lose their air bubble and sink.)
A craft knife or other small sharp knife.
A glass or other suitable container (Don't use a jar or other container with curved top that would allow flame from wick to come into contact with the glass.)
Short, 3/4 inch (18mm), wicks. (These can be purchased, made from cotton yarn, or removed from tea candles.)
Cooking oil. (Olive oil burns cleanly and relatively odorlessly. DO NOT USE ANY PETROLEUM BASED PRODUCT!)