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The use of kaolin clay in soap occurs for many different reasons. Among soap additives, it is one of the most common. Especially in shaving soaps, kaolin clay in soap provides skin slip and dries to a smooth, matte finish. Kaolin clay in soap can absorb both oil and water, and many use it as a soap additive for fixing scent, gentle skin polishing or just to improve the opacity and whiteness of a soap.

Kaolin clay is a fine textured, highly absorbent mineral compound mined in locations all over the world. About 50 percent of the kaolin produced is used in the making of paper, where it gives gloss to coated papers. In medicine, it is known for helping blood to clot and is embedded in certain types of bandages. Of course, everyone who has ever admired a porcelain teacup has seen kaolin ceramics in action. It is an effective tooth polishing agent used in toothpaste. Kaolin slurry is sprayed on crops to deter insects, and on apples to prevent sun scalding. It can be used to soothe an upset stomach and to remedy diarrhea. In ancient times kaolin was used to clean wool and fabrics, as it’s oil absorbent properties were already well known. Even in winemaking, kaolin has a place at the table — it is used to decrease cloudiness, especially in white wines.

When it comes to beauty, kaolin clay is queen. Present in nearly every product from primers and foundations to facial masks, toothpastes and deodorants, kaolin is a gentle and ubiquitous ingredient. Kaolin has a smooth, slippery feel even though it is a gentle exfoliant. Kaolin can also be used as an alternative to titanium dioxide for adding opacity and whiteness to soap, although it’s whitening power is less dramatic. Another use for kaolin’s oil absorbing properties is as a fragrance fixative in soaps. Many people soak their kaolin clay in essential or fragrance oil first, then add the clay slurry to the soap at trace.

For this article, I did a comparison of six bars of 100 percent olive oil soap. The soap ingredients were kept simple and basic to remove as many unrelated variables as possible. Olive oil soap is not noted for being very white by itself, so I chose olive oil to better display the whitening properties of both kaolin clay and water-soluble titanium dioxide. I started off with four ounces of plain, 100 percent olive oil soap for the first pour. Next, I added two teaspoons of kaolin clay dispersed in one tablespoon of water to four ounces of olive oil soap. The third bar contained two teaspoons of water-soluble titanium dioxide dissolved in one tablespoon of water. Both the kaolin and titanium dioxide powders were very fine and dissolved readily into the water with minimal clumping. A small, battery-operated drink mixer was used to further hydrate the two powders before adding to the soap.

The fourth bar of soap was comprised of four ounces of olive oil soap with the addition of two teaspoons of African red palm oil, coloring soap naturally a bright orange hue. The first colored bar had a slight translucent quality. The fifth bar of soap contained the African red palm oil plus kaolin clay hydrated in water as before. The sixth bar contained the titanium dioxide solution.

The results were very striking: in both the colored and uncolored soaps, the kaolin clay gave added opacity, although in the plain bar the overall color became slightly gray-beige, making it a bit darker than the original. In the colored soap, kaolin clay lightened the soap to a creamy beige-yellow shade. Titanium dioxide in the plain soap yielded a bright white, fully opaque bar. In the colored soap it created a sunny yellow shade.

Because olive oil soap is a slow curing recipe, I left the six bars of soap in the molds for a full week without disturbing. None of the soaps went through gel phase. At the end of one week, the plain uncolored and plain colored soaps popped out of the mold readily and maintained their shape well. Both the kaolin and titanium dioxide treated soaps were still too soft to remove without damaging the soaps, so I had to freeze them in order to release them from the molds. I believe the bars were softer because of the extra water content, not because of the additives. The addition of sodium lactate in the soap should help to counter the added moisture.

As far as lathering effects, the titanium dioxide bars did not have any noticeable difference from the plain bars.  The bars containing kaolin, however, had a silkier, more opaque and creamy lather. It rinsed away easily, but left a lasting silky feeling and a matte appearance to the skin. I compared shaving with the six soaps, and found that the kaolin-containing soaps did offer a noticeable decrease in the feeling of razor “drag” against the skin.

For my final experiment, I used a fragrance oil that is known to me to fade significantly in the finished soap. I prepared a three-pound loaf of soap batter and divided it in half, adding one ounce of fragrance oil to each half. The difference was that in one batch, the fragrance oil was first mixed with two teaspoons of kaolin clay. The fragrance was added directly to the soap batter for the second half. After one full week of curing, I noticed significant scent fade in both soaps, but the plain soap was faded a bit more. My conclusion is that there is something to the fragrance-fixing benefits of clay, although the difference was not dramatic.

All things considered, I would use titanium dioxide if I wanted the benefits of whitening and opacity, whereas kaolin would be reserved for performance — the slip it gives to shaving soaps is significant and very helpful in preventing bumps. If I am searching for something to lighten an added color, the kaolin and titanium dioxide do a similar enough job that I feel they can be used interchangeably for this purpose, however the titanium dioxide keeps a truer color in the finished soap. For scent fixing, I still prefer the perfumer’s method of using top, heart and base notes in a scent in order to render it long-lasting.

Have you used kaolin clay in soap making? What goals did you have for your finished kaolin clay soap? Did the addition of kaolin help you to meet those goals? Please share your experiences!