Two ways to build a pattern
Layering and embedding are both ways to make a bar with defined areas of color, rather than a single shade or a swirl. In layering, you pour one color, then another, so that the finished bar shows stripes. In embedding, you set solid pieces of soap, often cut shapes, into a fresh batter so they appear as shapes inside the bar.
Both techniques depend on the same thing: the state of the batter. Too thin and colors run together. Too thick and the soap will not settle, and gaps form.
How layering works
You split the batch into portions, color each one, and pour them in sequence. The main question is timing.
Pouring while thin gives layers that blend slightly at the boundaries. That can be attractive, but it is hard to control, and the colors may mix into a muddy middle. If you want crisp lines, thin batter is a challenge.
Letting each layer thicken first. For sharp layers, makers often wait until the first layer has set enough to hold the next one, such as when it resembles a soft pudding or has a thin skin. Pouring the next layer gently over the back of a spoon spreads the weight and keeps it from punching through.
Letting layers firm too much. The opposite problem is waiting so long that the first layer becomes hard and dry. Then the second layer may not bond properly and the finished bar can split along the seam. This is a form of soap separation, a problem described in its own article. If you pause between layers, do not wait so long that the surface hardens, and a light spritz is sometimes used by makers to help bonding, though it should be done sparingly.
Two other points:
- Thicker batter at pour. Starting with a batch that traces thick, with a recipe that is slow to set, gives more control. If your recipe moves quickly, perhaps because of the fragrance you added, it may seize or accelerate. See our article on soap seizing for why this happens.
- Even pouring. Pour near the surface, close to the earlier layer, so as not to disturb it.
Layers can also be tilted, by propping one end of the mold on a folded towel for the first pour, then pouring the next layer after leveling it. The result is diagonal stripes.
How embedding works
An embed is a piece of already-made soap placed in a new batch. It might be a cut strip, a shape cut with a cookie cutter, or a small chunk. Embeds are often made from a soap that has been cut and hardened, from melt and pour, or from leftover trimmings.
Some practical points:
- Firmness matters. The embed should be firm enough to keep its shape in the batter. Cold process embeds usually need several days or longer to harden, depending on the recipe.
- Batter thickness. Medium to thick batter holds embeds in place. Thin batter may let them float, tilt or sink.
- Compatibility. Embeds of melt and pour in cold process soap are popular, but they can behave differently. Melt and pour contains additives that make it sweat and attract moisture, so in some bars the embed may look slightly different over time or leave a visible edge. The article on melt and pour explains the base.
- Placement. Place embeds with clean hands or tweezers. Pack batter around and between them so no air pockets remain. Tapping the mold on a towel helps settle the soap.
- Contrast. For a clear visual effect, choose embeds with a distinct color from the surrounding batter. A white embed in a deep brown bar reads boldly.
Cutting patterned bars
Layered and embedded designs are best revealed when the loaf is cut. Each slice shows a unique cross-section. Cut with a sharp blade or wire, and wipe the blade between cuts so colors do not drag across the face. If an embed tears or pulls, wait a day longer, as the loaf may be too soft. The article on cutting soap covers timing and tools.
Things that can go wrong
- Colors bleed. Some pigments migrate into neighboring layers, especially those that are water soluble. Test your colorants before a batch where sharp separation matters.
- Gel phase differences. If one part of the loaf goes through gel and another does not, colors may look uneven. Insulating the whole mold evenly helps. See the article on gel phase for more.
- Cracking along the seams. Large temperature differences between layers or embeds can add stress. Avoid putting a cold embed into a very hot batter.
- Embeds that dissolve or soften. A very wet or soft embed can lose its edges. Use firmer pieces.
Keeping it manageable
If you are new to patterned soap, try a two-color layered loaf first. Embedding is a nice second step. Keep notes on how thick the batter was at each pour, because next time you can adjust. As with any batch, work safely with lye, using protective gear, ventilation, a tested recipe and keeping children and pets away. Patterned soap should still be cured fully before use.