Days ago I saw this link on Facebook about making a rainbow cake loaf, it got me very excited! Normal people see cake, I see soap!
This is a very time consuming project, it needs to be made in multiple stages, actually very similar to baking a cake and then decorate it. To start, I went to home improvement store and bought a sheet of plastic corrugated panel, it's lightweight but non stick and not that hard to cut. I made myself a cheap mold so I can make a skinny loaf of soap.
I used banana blended in coconut milk to make the "cake." The speckles from banana is perfect for imitating an actual cake don't you think?
The next day I unmolded the soap and made some whipped soap for icing to cover all 5 sides. Curious about what whipped soap is?! Well, I got it covered, see this post about making whipped soap: How to Make Whipped Soap
The reason I used whipped soap for icing is so I would have plenty of play time to get it all smooth and pretty. And whipped soap texture is the closest to the real texture of cake icing or whipped cream. This is the time consuming part. After slapping on the whipped soap with a knife I started using a silicone scraper to smooth all sides out back and forwards many passes.
The last stage is the color drizzles. This is the part that went crazy on me. Splitting a very small batch of soap into 7 colors is not a good idea. I was not able to keep the soap batter fluid enough, it was more like icing than syrup. Instead of drizzling on the "cake" top, I had to improvise and scoop each color soap into a sheet of saran wrap each, scrunched up all sides, poke a tiny hole at the center and squeeze it like a pipping bag.
They look like rainbow worms crawling all over my cake soap!
Here is the cut to see how it looks like inside. Why not make a white cake inside just like the inspiration photo? Well,
my design concept is you only get to see a piece of rainbow right after a stormy sky, never see a rainbow in a perfectly bright sunny day!