Dark Vs. Light - The instructions say to put them in a dark place to grow. I put them in a semi-light spot, but it was still by a window. If I put them in a dark spot, then it would be hard to watch them grow, so I met the instructions halfway. Add to your experiment and see what happens if you put one in the dark and one in the light. I’m curious! Crystal Growing Chamber - Silicon cup that you can use to grow the crystals. You can also use a jar from home if you want, but more the “con” of that later. span itemprop="name">Not worth it!Bought this for my granddaughter at Christmas. Followed the directions to a tee. Crystals were growing and colours were great. The next morning most of the crystals had fallen off and felt very spongy. Would not recommend this.