Silicate minerals comprise approximately 90 percent of the Earth’s crust, and many of them are classified as clays. Clays are fine-grained natural rocks or soil materials that primarily contain hydrates of aluminum silicate, often in combination with other metals and trace organic matter.
Clays can broadly be classified as either crystalline or amorphous in nature. Those that have a layered or plate-like texture are referred to as phyllosilicates. The more common crystalline phyllosilicates clays used in personal care include hectorite, smectite, montmorillonite, kaolin, and mica.
Clays are normally produced by grinding mined ore then washing, treating and drying the powder. Geologic clay deposits are mostly composed of phyllosilicate minerals, containing variable amounts of water, trapped in the mineral structure. This moisture makes clays plastic in nature, but they become hard, brittle and non–plastic upon drying. Depending on where clays are found, they can appear in various colors including white, yellow, dull gray, brown and deep orange-red.
Clays have numerous uses in personal care products, such as thickening, suspending, stabilizing suspensions and emulsions, and absorbing oils. Clays are also used for pearls and as binders and disintegrants in tablets.
The most common clays used for thickening water-based products are smectite, hectorite, and montmorillonite, with smectite being the most efficient at generating viscosity and suspending solids. These clays have a platelet shape with a negatively charged surface and positively charged edge, and they develop a house-of-cards-like structure when dispersed and hydrated in water.
Typically, the best performance is attained using high-shear processing to hydrate and structure the clay. Good suspending properties are due to the shear-thinning, thixotropic behavior of clay dispersions, which increases the yield value or resting viscosity of the formulation.
Clays are often used in combination with gums and organic thickeners, such as xanthan, carboxymethylcellulose or carbomers, to synergistically increase viscosity and the yield value. The viscosity and stability of formulations containing the mixtures are normally significantly better than those made with individual components.
When using clays, it’s best to avoid the use of cationic ingredients because they can react and flocculate out of the formulation. Synthetic clays (sodium magnesium silicate) have also been developed with improved thickening and suspending performance; even clear gels can be formulated with this type of material.
Hydrophobically modified cationic clays are important ingredients used to gel oils, suspend solids in anhydrous formulations and help stabilize water in oil emulsions. These clays are made by reacting bentonite or hectorite with stearalkonium chloride, distearyldimonium chloride or quaternium 90. Typically, high-shear processing is required to make the oil gel along with a polar additive like propylene carbonate or ethanol.
The quaternium bentonite is preferred for making gels using low- to medium-polarity oils while stearalkonium bentonite is better for medium- to high-polarity oils. Kaolin, bentonite and montmorillonite are typically used in clay-mask formulations and as sebum absorbers. Naturally mined montmorillonite is also available in white, red and green colors.
Metal-coated micas or interference pigments are important ingredients commonly used as pearls and glitters in eyeshadow and lipstick formulations. They are made by depositing various layers of either titanium dioxide or iron oxide onto mica particles. When light hits the surface of these particles, it is reflected and refracted by the various layers, which results in multiple colors. By increasing either the thickness of the titanium dioxide or the iron oxide, a broad range of colors can be produced. The colors will change when viewed at various angles.
References:
Clay. 26 July 2016. San Francisco (CA): Wikipedia; [accessed July 2016]. https://en.wikipedia.org/wiki/Clay
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Hi… good & informative.. Would like to get more information. Want to make a clear gel ( Organic)compatable with Oil based Liquid soap & Sulphate free surfactant systems , Face wash/ Body wash/ Hair wash ; would like to make thick Oil Gel ( Organic) for Facial products… pl. suggest me.
I have rosacea so bad that it is getting in my eyes. I have tried the normal antibiotics and antifungal creams. I was hoping that I could buy some of the Kismet Clay Mask to see if this might be the direction to persue. Please let me know how to buy the clay mask.
Sincerely,
Shelley Hibler
[email protected]
Hi, Shelley:
I’m sorry. I can’t help. I suggest seeing a doctor.
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