I used activated charcoal to color the black part of the soap, and it really dried out the black layer. You can see little cracks in the black part. Also, I should've mixed it with a small portion of soap before incorporating it into the batch, but overall, I'm pleased with how it turned out.
For the colors, I used Mica's from Brambleberry, and it's scented with Brambleberry's Coconut Citrus Sorbet. I think it looks (and smells!) like a Hawaiian volcano.
I used a flexible cutting mat that I cut to the size of my mold, but it was too flexible, and I had a hard time getting it to stay where it belonged, and not bend under the weight of the soap building up. After I was done, I went to my parents' house and cut a custom piece of sheet metal so that I can do this again with a better divider. The bar of soap at the top of the picture that has two swirls in it: that one was on one of the ends of the loaf, and as the divider slid back and I slid it forward again, this is what happened. I think it's pretty cool!
I really learned a lot from this challenge, and can't wait for the next one! Thanks GreatCakesSoapWorks for the awesome tutorial!
By the way, here's the picture of the original: this is what the challenge goal was. Such a fun project!