Natural clays have been used for millennia in skin care for their cleansing and purifying properties. They have become popular in soap making, because they are considered a natural alternative to colouring soap, and they come in a variety of colours, most commonly green, yellow and varying shades of red. The different colours depend on the mineral composition of the clay, which is determined by the source rock from which they clay was formed through the processes of weathering and erosion. Note clays are basically dirt! The main types of clays that are used in cosmetics are illite clays (i.e. French clays), montmorillonite clays (Bentonite and Fuller’s Earth) and kaolin clay.
What makes clays unique is their cation-exchange capacity (CEC) – the ability to adsorb and exchange cations (positively charged ions). Montmorillonite clays have the highest CEC rate, and kaolin clay the lowest, with the illite clays somewhere in between.
In skin care, this means that clay can remove positively charged toxins and pollutants from your skin.
Montmorillonite clays possess the highest cation-exchange capacities. They are formed from weathering and erosion of volcanic ashes, producing hydrated (sodium calcium aluminum magnesium) silicates, which contain many valuable trace minerals. Montmorillonite clay is the principal ingredient of bentonite and Fuller’s earth. These clays are the only ones to have expanding (swelling) capacity – meaning they absorb water, unlike other clays, which are just diluted with water. This is a particular useful property in shaving soaps, because it adds slip and glide to the soap.
Kaolinite clay, on the other hand, is a non-swelling clay with the lowest cation-exchange capacity, and is the most gentle on the skin. These aluminium silicates are the main component of kaolin clay, which gets its name from the Chinese word, “Gaoling”, meaning ‘high ridge’. Kaolinite clays are formed by weathering or hydrothermal alteration of aluminosilicate minerals, common in feldspar rocks.
The CEC rate of the illite clays lie somewhere between kaolinite and montmorillonite clays, depending on their mineral composition. Similar to kaolinite clays, they are also formed by decomposition of feldspar rocks, but under high pH (alkaline) environments. These non-swelling, mica silicates are the most common of clays and are widely distributed in marine shales and sediments. Varying mineral compositions, which may include calcium, sodium, magnesium, potassium, silicium, manganese, phosporous, copper, and/or selenium, give rise to the many various colours and properties of the different illite clays.
A common misconception is that clays soak up or absorb oils and fats, and are thus beneficial for oily skin. Unfortunately, most clays don’t have the ability to draw excess oil from your skin, with the exception of calcium bentonite. They do, however, gently exfoliate the top layer of your skin, and remove dead cells, dirt and some of the excess oil with it. In addition to the exfoliation, they also draw water from your skin, which is why clays are not recommended for particular dry and sensitive skin.
The many benefits of using clay in soap:
- exfoliates and smoothes
- removes toxins and pollutants
- stimulates and brightens
- adds slip (for shaving)
- contains valuable minerals
- natural colourant
Using clays in cold process soap
Because of their various properties, clays are a popular additive in soap making. It is a great option if you are looking for a natural colourant. The rule of thumb is to use about 1 teaspoon of clay to 500g of soap, you can add more, but be aware that adding clay can speed up trace. You can add the clay either directly to the lye water, which will intensify the colour, or add it to the soap at trace. However, clays absorb liquid, so it’s important to wet the clay before adding it to the soap mixture. I like to dilute 1 teaspoon of clay in 1 tablespoon of water and mix it into a slurry. Wetting the clay also helps disperse the clay more evenly throughout the soap, reducing spotting.
Using clays in melt and pour soap
Clays are also great to add to melt and pour soap bases. The usage rate in melt and pour soap bases is around 1 teaspoon per 500g soap. I would be careful of adding too much, because it will make the soap very thick and difficult to work with. To avoid clumping and disperse the clay evenly in the soap, I like to dilute 1 teaspoon of clay in 1-2 teaspoons of 99% isopropyl alcohol. Using alcohol also has the benefit of reducing bubbles in your soap. Don’t worry about the alcohol, the heat of the melted soap will evaporate the alcohol leaving only the clay behind.
Types of clay
Bentonite clay (also Sodium bentonite)
Bentonite clay is a sodium bentonite, which is created from volcanic ash. It has a unique property of absorbing water (it can swell up to 14 times its weight!), which will add slip to the soap, particular useful in shaving soaps, as it allows the razor to glide smoothly over the skin. Bentonite clay has a grey to cream colour.
Best used in shaving soaps
Fuller’s earth is another bentonite clay, but instead of sodium it contains calcium, which makes it the only clay to absorb oil, and is often used in combination to clear oil spills. Bentonite clays also have the highest CEC rate, meaning it has the highest rate of removing toxins, impurities and pollutants from your skin, which makes it ideal for oily and acne-prone skin. Colours range from brown or green to grey and cream.
Use in soaps for oily and acne-prone skins, but never on dry and sensitive skins!
Also known as rhassoul clay or Moroccan red clay, this ancient volcanic clay is mined from the lacustrine (lake) sedimentary rocks of the Atlas Mountains in Morocco and has been used since the 8th century by Moroccan women in hair and skin care. The name ghassoul comes from the Arabic word “ghassala”, meaning “to wash”. Like the other montmorillonite clays, ghassoul clay absorbs water, but because of its very fine texture, it feels smooth and lubricating and has a very high absorption rate, which makes it extremely effective at detoxifying and purifying the skin and a gentle exfoliant, clearing clogged pores, removing dead cells and stimulating circulation. And with its high silica content, ghassoul clay is considered one of the most luxurious cosmetic clays and is used in top spas around the world.
Soaps containing ghassoul clay leave the skin looking radiant and rejuvenated.
French Green Clay
French green clay, also known as marine clay, is an illite clay formed from sea sediments, which receives its green colour from decomposed seaweed and algae, and is considered a bio-mineral rich in minerals and phyto-nutrients.
French green clay is an excellent additive to soaps, but be aware that the green colour turns grey-green in soap.
French Yellow Clay
Yellow illite clay is also similar to green illite in its cosmetic uses and properties, and but differs from the green by a higher content of iron oxides. It is similar in its cosmetic uses and properties to the green clay.
In soaps it is mainly used as a natural colourant.
French Red Clay
French red clay receives its colour from its high concentration of iron oxides, which increases its strength of removing toxins, pollutants and other impurities from the skin. It is also an excellent exfoliant, removing dead cells, unclogging pores and smoothing the skin, leaving it looking rejuvenated and radiant.
An excellent additive to shower soaps, particular for use on upper arms, back of thighs and stomach. Also used as a natural colourant.
French white clay
White clay has similar properties as the other illite clays, but is not as mineral-rich.
Use in soaps when you want the exfoliating and detoxifying benefits, but without adding colour to the soap.
French Pink Clay
French pink clay or rose clay is often a blend of red illite and white kaolin clays, and its colours range from a light pink to a rich rose or even orange shade. The colour is determined by the amount of iron oxides in the red illite clay. Because of the added kaolin clay, it is considered the mildest of all illite clays. Pink clay is a very mild detoxifier and a gentle exfoliant and is especially suitable for sensitive, mature, and dehydrated skins.
In soaps, it is used as a natural colourant but also as a mild exfoliant.