What Is the In-the-Pot Swirl?

The in-the-pot swirl (often abbreviated ITP swirl) is a soapmaking technique where you create your design inside the mixing vessel before pouring into a mold, rather than doing design work in the mold itself. It's one of the most beginner-friendly decorative techniques because it doesn't require precise pouring or expensive tools — and the results are beautifully organic and unpredictable.

Every ITP swirl bar is unique. No two pours are ever identical, which is part of the charm.

What You'll Need

  • Your prepared soap batter at light trace (thin is key — thick trace won't swirl well)
  • 2–4 skin-safe soap colorants (oxides, micas, or clays)
  • Small cups or containers for dividing batter
  • A chopstick, skewer, or thin spatula for swirling
  • A loaf mold or individual cavity molds
  • A stick blender and spatulas

Choosing Your Colors

Color selection dramatically affects the final look. A few guidelines:

  • Start with 2–3 colors until you understand how they blend together in soap.
  • Use colors with enough contrast — light and dark, warm and cool.
  • Micas give vibrant, shimmery results. Oxides and ultramarines give matte, earthy tones. Clays add natural, subtle color.
  • Pre-disperse your colorants in a small amount of lightweight oil (like sweet almond or fractionated coconut oil) before mixing into the batter. Use approximately 1 teaspoon of colorant per tablespoon of oil.
  • Avoid colors that are known to morph in cold process soap — pink micas can turn brown, and some reds fade. Research your specific colorants.

Step-by-Step: The ITP Swirl

  1. Bring your soap batter to a thin light trace. This is critical. If the batter is too thick, it won't flow and swirl. If you're using a fragrance oil, test it first on a small amount of batter to make sure it doesn't accelerate trace.
  2. Divide your batter. Pour roughly equal amounts (or intentionally unequal for a more dynamic look) into separate containers — one per color. Reserve about one-third as your base color in the main mixing vessel.
  3. Add colorants. Stir each container's pre-dispersed colorant into its batter thoroughly. Stick blend briefly if needed to ensure even color distribution.
  4. Pour colors back into the main pot. Pour each colored portion into the main pot in deliberate streams — pour down the center, or in lines, or in concentric circles. Don't stir yet.
  5. Swirl. Using your chopstick or skewer, make slow, deliberate figure-eight or S-shaped strokes through the batter. Don't over-swirl — 4 to 6 strokes is often enough. Over-mixing blends the colors into mud.
  6. Pour into your mold in a slow, steady stream from one end to the other. The swirl pattern will shift slightly as it pours — embrace it.
  7. Cover and insulate as you normally would for your recipe.

Variations to Try

Taiwan Swirl

A variation of the ITP swirl where you use a skewer to make a series of straight lines in alternating directions through the poured batter — creating a feathered or chevron effect on the cut face of the bar.

Hanger Swirl

After pouring into the mold, drag a wire hanger or straightened hanger tool through the batter in a systematic pattern. Spectacular on loaf molds when you look at the top surface.

Two-Color ITP

Using just two high-contrast colors (like white and deep indigo, or cream and burnt orange) often produces the most striking, graphic results. Simplicity is powerful.

Troubleshooting

  • Colors all blended together: Batter was too warm, you swirled too much, or the fragrance accelerated trace. Next time, work at a cooler temperature and reduce swirling passes.
  • No visible swirl in the cut bar: Colors were too similar in value (lightness/darkness). Increase contrast or use more distinct hues.
  • Muddy, brown result: Complementary colors mixed together cancel out. Avoid pairing opposite colors (red + green, purple + yellow) in the same swirl unless separated by a neutral white.

The Joy of Imperfection

Part of what makes handmade soap beautiful is its variation. No machine-made bar has the unique pattern of a well-executed ITP swirl. Photograph your cut bars before they cure — the fresh soap colors are often most vibrant right after cutting — and don't be discouraged by unexpected results. Each "mistake" teaches you something that will make the next batch even better.