I have had this experiment bookmarked for a while and we finally got round to it last week. We started off by collecting the equipment...
bamboo skewers with the pointed end cut off
small jug for pouring
First you need to make the sugar mixture, I measured two bottles of water into a saucepan, with the sugar added this actually made enough solution for 4 bottles. Bring the water to the boil and add a cup of sugar, reduce the heat and once the sugar as dissolved add some more, spoonfuls at a time. You do end up using a LOT of sugar, keep adding the sugar until no more will dissolve in the solution.
Be careful doing this with a small child around, the sugar solution gets very hot. Pour the solution into small jugs or bowls, then add the food colour to each jug, it needs to quite strong in colour.
Once it has cooled a bit, pour each colour into a clean bottle, for easy clean up put all the bottles on a tray.
Attach a clothes peg to the end of each bamboo skewer, take a skewer and dip it into the solution then roll in sugar, allow it to dry, we noticed that the skewers that were given longer drying time grew better crystals.
Carefully put the skewer back in the bottle, position it so that it doesn't touch the sides or bottom.
Place the tray in a sunny spot and somewhere where it isn't likely to get knocked over and wait.... and wait...
It takes about 3 days to get a good growth on the skewers...
We put our experiment on the sideboard next to the dining table so it gets checked every mealtime.
How does it work? There are two different methods that contribute to the growth of the crystals on the bamboo skewer. First, by heating a saturated sugar solution (a solution in which no more sugar can dissolve at a particular temperature) and then allowing it to cool you have created a supersaturated solution. A supersaturated solution is unstable—it contains more solute (sugar) than can stay in a liquid form—so the sugar will come out of solution, forming what's called a precipitate. This method is called precipitation.
The other is method is evaporation. As time passes, the water will evaporate slowly from the supersaturated solution. As the water evaporates, the solution becomes more saturated and sugar molecules will continue to come out of the solution and collect on bamboo skewer. The rock candy crystals grow molecule by molecule. Thank you google for helping me out there, chemistry was not my strongest subject at school.