If you're waiting for somebody who knows what they're talking about, that would not be me.
However...
It would help to know what you mean by layer. Do you want your layers to be different colors or different soaps? It must be different soaps since for different colors you could either divide your batch and color the parts separately then pour and hope they don't mix too much. I've seen lots of pictures in Dr. Robert McDaniel's "Essentially Soap" where he says, "About half the mold was filled with soap colored using ... and then an uncolored soap was poured on top of the first layer. If you don't want mixing, the original layer must be thick enough to completely support the subsequent layers." It was clear from the context that both layers were the same batch except from colors.
Presumably you would wait a little more time after trace before pouring to get a thicker layer?
Perhaps you could do two batches, either the same soap different colors, or even different soaps, do the second batch a few or several hours after the first batch, don't know if this would work or whether it would be worth the trouble over the first method.
I'm considering doing a layered soap from Melinda Coss's "Gourmet Soaps Made Easy" where she makes Pina Colada soap, a layer of CP made from coconut oil and a little cocoa butter, scented coconut. She lets the CP firm up for several hours, then makes a batch of M&P dyed yellow and scented pineapple. "Wipe or spray the surface of the coconut soap base with witch hazel. Pour the glycerine soap on top of the base. Gently shake the mold so that the topping is evenly distributed. Leave to set." It looks good enough to eat!!!
Well I hope these ideas help contribute to the discussion.
