Plastic and Stainless Steel

1. Plastic and stainless steel are the best mold materials. Glass and china molds are acceptable as a last resort, but the soap in them won't be easy to extract, and mold breakage is always a concern.

The small plastic containers in which some types of cheeses and dairy spreads are packaged make great molds for larger bars and can be found in both round and rectangular shapes.

Aluminum molds are risky only if your soap hasn't cured properly and still has actively caustic lye in it; they work very well with properly cured soaps.

2. Mold materials must be able to withstand the high temperatures of hot soap. Empty plastic cookie trays, for example, sometimes have wonderful designs on their bottom surfaces, but beware! These nondurable trays will melt or deform when soap is poured into them.

3. Flexible molds are preferable to ones that are completely rigid, as the bars will be easier to remove.

4. Try to be practical when it comes to the size and depth of the mold. Though a shape may take your fancy, if the mold is too shallow or too small, the soap that you mold in it will just end up slipping down the drain.

Also keep in mind that soap shrinks as it dries. Aim for variety in your soap-mold collection, and be sure to include some for making large bars, some for making medium-size hand soaps, and some small ones for making guest soaps.

5. The open end of any mold must be larger than the closed end, or the hardened soap will be trapped inside. Avoid straight-sided molds, or you'll end up having to pry the soap out with a knife, marring the bars as you do.

Plastic juice containers, for example, just won't work, unless you're prepared to destroy the mold by cutting or peeling it away. Occasionally, soap makers do choose to treat their molds as disposable.

6. Select molds with enough detail on their inner surfaces to provide beautifully expressed soaps, and try a few basic molds before you invest a fortune in ones you may never use. Add to your collection when you're more experienced and know more about what you're looking for.