Growing Crystals

Ethan just finished up his 5th grade Science project. He chose to compare the growth of three kinds of crystals: sugar, salt and alum. The project took up a corner of the kitchen counter the past couple of weeks as we watched the crystals grow. We had to re-do part of the experiment because some crystals were growing on the bottom of the jar instead of on the string that he put into the solutions. He was awarded the 'Mad Scientist' award for his project.
Here is Ethan's summary of each crystal: Salt: It was the tallest crystal. At first, the crystal grew up the string on the part that wasn't in the solution. It was the roughest crystal and the lightest by volume.
Sugar: Sugar was the largest crystal in the first experiment. It displaced 15mL of water. It tasted really good.
Alum: Alum was the smallest in the initial experiment because it all grew on the bottom of the jar. We reheated the solution so that all of the crystals dissolved and put in a starter crystal. Overnight, it grew large and displaced 24mL of water. It won the experiment.