What you will need...
1. Pot for melting wax
2. Cooking thermometer
3. Pebbles (can get from local fish/pet store)
4. Candle wax
5. Wick
6. Bowl
7. Object to create candle shape (We simply used a smaller bowl.)
8. Wooden spoon for stirring wax
9. 2 x wooden skewers
10. 1/2 cup of water
11. Piece of paper
12. Sticky putty
13. Spoon
14. Jug
15. Chisel

A few pics followed by the write-up

Step 1. Prepare the pebbles
Prepare the pebbles by adding a small amount of water. Mix around with your hands to make sure all pebbles are damp. This trick helps the pebbles hold their shape. If you find you've poured in too much water, just drain the pebbles and then use.

Step 2. Make the mold
Flatten the surface of the pebbles. Then using two hands, press the object you're using to shape your candle into the bowl of pebbles to make the mold. Slowly pull out the object once you are happy with the shape or the depth you pushed it in.

Step 3. Prepare the wax
Now prepare the wax. Melt all your bits of wax in a pot. Keep stirring on a medium heat as the wax melts. Never leave it unattended while melting. Make sure as you are doing this, you safely remove all wicks from the old candles you are melting. For example, pull them out with tongs. Once all the wax is melted, put in your cooking thermometer and heat the wax to a temperature of 275 degrees Fahrenheit or 135 degrees Celsius. Note that this heat is a bit hotter than is usually recommended for making other candles.

Step 4. Prepare the wick
Prepare the wick by dipping a piece of wick into the hot melted wax and then lay it out straight on a piece of paper. Allow to set

Step 5. Pour in the wax
Transfer the melted wax from the pot into a jug. Pour the wax slowly from the jug into the pebble mold. Use the back of a spoon to disperse the pouring wax and avoid breaking the mold.

Step 6. Top up the wax
When the wax connects with the damp pebbles it will make a hissing sound and the wax will bubble. This is normal. Top up the wax once or twice because the wax level will lower as it seeps into the pebbles. (This creates the outer crust of the candle). You may have to reheat the remaining wax if you have a particularly large mold, as the seeping process could take a while.

Step 7. Add embellishments
Allow the wax to form a skin on top. In our case this took about 20 - 30 minutes. Pay close attention that it does not become too hard before you do the following. This is now a good time to add any embellishments (e.g. pebbles or shells) to the surface of your candle. Press them gently into the skin, ensuring the bottom parts of the objects reach the melted wax below so they set in place. Be careful not to disturb the skin too much as the skin will be the finished look on top of your candle.

Step 8. Add the wick
Taking a wooden skewer, press it through the top skin into the middle of your candle to create a hole for your wick. Push the wick through the hole down to the pebbles on the bottom. Keep the wick in place by placing it between two wooden skewers. Keep the skewers tightly together by using sticky putty on each end or by tying with string.

Step 9. Leave the candle to set
Rest the skewers across the top of the bowl and leave there until the candle has set.

Step 10. Separate the candle from the bowl
When the wax has cooled, check around the edges to make sure the mold will come out when tipped up. Use a knife or sharp object to run around the sides to clear any wax that is attached to the sides of the bowl.

Step 11. Shape the candle
Tip bowl and gently guide out the candle. Remove excess pebbles by running your hand around it all, and then use a chisel to shape the outside shell. How much you chip away is totally up to you and determined by how much wax has gone through the pebbles. No two candles will be the same.