I haven't done a lot of soap art, just a few basic swirls. Because I use natural products and try to keep my costs down it is a bit limiting. Unless I have reason to do something a bit more involved, I will just use turmeric for a basic swirl or colouring as it has so many skin/health benefits.
There are lessons on You Tube with some really impressive results. I have seen colours that are incredible but have to admit wondering if they make you glow in the dark and Geiger counters tick.
This is very, very basic but will show you what a non professional can do with no practise.
The black soap is coloured with Aussie Black Clay and is Man Soap for shaving.
Palm Kernel Oil made the round soap at the right very white.
The bar at the back is Goat Milk with turmeric.
The green swirl in the centre milk soap wasn't natural colour.
This soap can't be stored for extended periods as the colours fade (the spirulina quicker than the turmeric).
This was done hot process. I separated two cups of hot soap and mixed in the colours (mixed in a bit of water) I layered the coloured soap in amongst the uncoloured. When the mould was filled I used a tablespoon to stir in a circular motion from the top to the bottom moving along the mould. I repeated this twice and was very happy with the results.