Don't know if I'm using the right term but I have some soap that I made using glycerine from biodiesel. I made it a few months ago but would like to melt it back down to pour into a loaf mold that I made. Also I'd like to add some scent and possibly some craft store m&p glycerine to it to firm up the bars some. Can I do this or am I stuck with 'em? Also should I use a double boiler?