1. First you need to dye some soap. You’ll want small amounts of a variety of colors. Small plastic cups would work for this, but I used silicon muffin cups. (I never use them for baking anymore, but a bonus was that the soap really cleaned up old stains!) If you have them, individual silicone muffin cups would be perfect for this.
Decide on what colors you want your rocks to be, melt down small amounts (1 to 2 oz) of chopped up soap, and add dye of various colors. If your soap starts to solidify before you’ve mixed in the dye, just heat it up again in the microwave. Initially it took about 30 seconds of heating to melt, and then 10 to 20 to reheat. After you’ve mixed in the dyes, stick the soap in the freezer to let it solidify.
I used various combinations of liquid dyes and powdered makeup. If the powder wasn’t already loose, I scraped it off in thin layers with a knife. The color showed up in the opaque soap, but shimmer didn’t as much. Sometimes the powder stayed a bit clumped up, but I thought that was more realistically rock-life sometimes, so I went with it.
Below, I started out with pink, peach, and red shades using just liquid dyes in the white and clear soaps. These are actually from my first attempt, which I chopped up and reused, but you get the idea.