I have a lot of soap shavings left over and want to remelt and allow students to carve another piece. I'm hoping to add something to make it a bit harder, more carvable. The soap scraps are Ivory soap.
You need to use oils that dry hard. Olive and castor oil are two good choices.
I just add regular Olive Oil to make my bars hard again but it takes experimenting to find out how much to add and I did not write my amount down. It takes more than you would think and will be a little "soft" when first made but does harden slowly. Letting soap cure takes longer with oil - may take 2 -3 weeks.
Try beeswax if you can get some but use less than 10 percent of it in your entire mix ratio.
you could also use glycerin, which is used in making soap to begin with, and is available at many stores