The double boiler method does melt glycerin soaps, but takes some time. Shredded standard shaving soaps don't melt, but usually become softer when mixed with a small amount of water. They don't seem to be damaged because the heat is fairly even and gentle.You can't microwave a tallow based soap like Arko - will destroy the product. You need to use as-is, as ClemsonTigerz has done, grate it (see link to my earlier post on this above or melt in a double boiler (not sure I've seen anyone do this). Some have dissolved their soaps in water and then blended.