You can also use a previous soap and cut it up into slivers or chunks or triangles. I save the beveled ends of my soaps. Sometimes if the soap is still soft I roll the bits that I have shaved off into soap balls or if they are too hard I save them for confetti soaps.
This month Amy, of Great Cakes Soap Works, has made the challenge about using these embeds in a new soap. I used my soap balls in a soap last summer that turned out nicely - below is the photo.
Here are bags of soap balls in varying shades of browns, yellows and greens. I decided to do a layered soap using four different colors: cappachino mica, copper mica, green moss pigment and yellow oxide.