You will need:
1 cup rubbing alcohol
2-3 cups water
3-4 drops blue food colouring (optional)
2 large ziplock bags
Mix all ingredients in one ziplock bag. Push all the air out and seal (don't suck it out... haha... the fumes are strong!). Then place inside the second bag (just in case it leaks). Place in freezer for a few hours. If it doesn't seem to be freezing at all, just add a little more water. If its freezing too much, add more rubbing alcohol.