Molds for Soap Casting
One of the most exciting parts of soap casting is choosing your molds. Here are a few of the different options. (Tube molds are a special type of mold, with their own techniques, which will be described in the next section.)
Some techniques use block molds. The big block of soap that comes out of such a mold will be sliced into bars. You will also use block molds when making soap of contrasting colors to combine in other projects.
If the molded shape isn't important to your project, you can use pretty much anything as a block mold. Most serving-ware containers do very well. Keep in mind that you will see all the details of the container in your end product, so you'll have bumps, curves, mold marks, and lines in your bars. Those can be a pleasing part of the handmade soap experience. You can, of course, trim the odd bits with a dough scraper, paring knife, or cheese plane.
You can buy domed or “log” block molds created especially for soapcasting projects that are meant to be sliced like loaves. You can also use a plastic-lined or stainless steel baking loaf mold. These are great for multistage pours where you pour some, place some, pour some more, then cool and slice.
Bar molds can be simple rectangles or exquisite carvings transformed into vessels for creating beautiful soaps. You can find a growing number of suitable molds at craft and some mass-market stores. The Internet is an invaluable resource, as you can find molds that are sturdier and of a wider variety.
Generally, your casting soap will readily release from a bar mold. If it's a little stubborn, you can put it in the freezer for about ten minutes. The soap will contract and pull away from the sides of the molds, making for easier release. Some soapmakers use a silicone or cooking spray, but this isn't usually needed.
You can forage in your kitchen for all kinds of interesting molds, such as ice cube trays and plastic gelatin molds. Don't forget the recycling bin. The bumpy bottoms of plastic soda bottles make very interesting shapes. Cut the molded shape away from the rest of the plastic with heavy kitchen shears. Be sure to protect your hands as the edges can be sharp.
If you're going to use your molds only once in a while, the lighter gauge plastic of craft-store molds is perfectly fine. Be sure to treat them gently and wash them thoroughly in warm water and detergent. Dry them flat so they don't warp.
Molds made from heavier gauge plastic will last considerably longer, but they still need to be well cared for. Any mold will eventually crack under repeated use, but if you take good care of them, your molds will help you make beautiful soap for a long time, batch after batch.
Tray Molds and Beyond
A tray mold is a single-cavity mold with score marks for guidance in cutting your soap into bars after unmolding. Some have designs, too, such as lavender stems and animal figures. These are a beautiful hybrid of bar and block molds.
Basic casting soap setup
There are various three-dimensional molds available, as well. You can use two-part molds that you fasten together, seal, and pour. When the soap is hard, you take off the clips and release the form. You'll need to clean off the mold lines for a finished look. There are also flexible vinyl molds that you pull away from the sides and top, and silicone molds that you stretch and peel off the hardened soap.