So I ruined 2 soap pucks trying to microwave them to melt into a container. I was told that glycerin based soaps can be melted as long as you do it in short 5 second intervals until it's melted. I did this easily with my col conk soap but it didn't work with a couple of soaps that on the ingredients list said it had glycerin. Including Williams soap. Why is it that the soaps didn't melt but instead get extremely hot on the inside and soap began busting out from the center while the outside looked perfectly fine.
One general rule of thumb is tallow based soaps do not melt. Williams is in fact tallow based. The tallow ingredient reacts differently to heat and does not break down in the fashion that a glycerin soap does. An alternative to melting a tallow soap is to grate it with a cheese grater into the container of your choice and press it down firmly with your finger tips to mold it into the container.
Just because the soap has glycerin as an ingredient doesn't mean it's a "glycerin soap". A melt & pour glycerin soap ingredient list will have some tell-tale ingredients in it like wheat protein, maybe triethanolamine, sodium laureth sulfate, propylene glycol, sodium cocoyl isethionate...it depends on the manufacturer. Hard tallow based soap can't be melted, but soft artisan soap usually can be, with care.
Hard tallow based soap can't be melted in the microwave, but can be melted in a double boiler, with care (this is called rebatching) this is how triple-milled soaps are made. It's easy to screw this up and ruin your soap, which is why the grating method is always recommended to shavers. The big downside to rebatching is you will lose any fragrance the soap had, which is why fragrance is added just before the final pour in triple-milled soaps. This is for the other members, eyebright. I'm sure you know all about this. You sound as though you've been around soaps a while.
