This'd make a nice home-made present for grandparents or something like that, but kids should not attempt this without an adult's help.
You'll need the following:
A glass bottle, any size or type
A load of candle wax from new, used or dead candles
A candle wick (or 100% cotton string)
A small weight such as a fishing weight or washer
and you'll also need:
Cooker hob to melt candle wax
A container to melt candles in, I'm using a fizzy drink can with the top chopped off
Gloves or something to handle the hot container with
A hammer or something to break glass with.
Step 1: Preparation
Cut a length of wick that is longer than your bottle's length, you can shorten it after.
Tie a weight to the bottom of the wick, this will help it stay straight.
Have everything close to hand and you'll need to work fast to make sure the wax doesn't harden.
Step 2: Melting the Wax
I've collected candle leftovers for a while and hopefully have enough to fill up my bottle.
After putting all the wax into your container, put it on a gentle heat and let everything melt.
I put my can directly on the hob, but you can put your container in a saucepan of water, that way the wax will be less likely to burn as you heat the water
Wax can ignite if it gets too hot, so don't leave it unattended, melt it slowly and once it's melted, move on to the next step straight away.
Step 3: Pouring the Wax
As soon as the wax is in the bottle, lower your wick down the bottle gently and feel for the bottom.
To keep the wick straight you can either hold it very still for a long time, or if you don't want to be standing there for ages, you can drape it over the side of the bottle (careful, it may be hot), and then use some masking tape to secure it, making sure the wick doesn't lean over to one side, and instead, comes straight out the top of the bottle.
As the wax hardens, you'll find the wax level shrinks. You can fill it up with more molten wax as it hardens.
Now wait for the wax to harden, when it does, the glass bottle should be cold to the touch.
(did you remember to turn off the hob?)
Step 4: Smash the Bottle!
Once you're happy the wax has hardened, it's time to sacrifice the bottle.
Using a hammer, or drill, or something else like that, gently (very gently, or you'll break the candle) break the glass and make sure you clean it all up.
Now you need to trim the wick down, leaving about 1CM free.
You should now have a bottle styled candle ready to be lit.
Step 5: Finished Candle
The first candle I created wasn't a very appealing colour, which was down to using too many different colours to create it.
You can experiment with mixing wax colours, or even using scented wax from either scented candles or adding a few drops of essential oils or the like.
I hope you enjoyed this instructable, please rate and comment.