More Than Just Melting and Pouring
You can buy a bar of glycerin soap at the grocery, bring it home, cut it up, melt it in the microwave, pour it into a little plastic storage container, cool it, pop it out, and have a bar of soap. That is soap casting at its simplest. But it is just the beginning. The soapmaker can manipulate the plain soap base in an incredible variety of ways. Making additions and altering the shape of the soap are the bare bones of the procedures.
Before you begin your soap-casting endeavor, you'll need to estimate the number of ounces of soap needed. To do this, fill the molds with water and pour it off into a gradated glass measuring cup. If you have two cups of water, you'll need approximately one pound of soap. It is better to overestimate than not have enough. Have an extra container handy in which to pour the overflow. You can always use it for another project.