KAOLIN VS TALC
Many of the customers have confusion over difference between kaolin and talc.
They are both fine white powders that come from digging a mineral out of the ground and refining it. If you take a microscope and look at the particles close-up, they both look like tiny flat plates, which are called platelets. This platelet shape makes them good at cutting out the light, which is why we put them into paints and ceramic glazes to help with opacity.
Kaolin and talc have a lot more in common: They are both inert, which means they take no part in chemical reactions. They are also both insoluble in water and hence they do not dissolve.
Although both are minerals, only kaolin is called clay. In fact kaolin’s common name is china clay. The common name for talc is talcum powder and it is the softest mineral on earth. That must be why it is chosen for use as baby powder.
Kaolin is also a soft mineral and comes just above talc on the Mohs hardness scale of minerals:
|Mohs hardness of minerals
The talc is much whiter compare to Kaolin.
The biggest difference between Talc and Kaolin is that talc stick to your blazes while kaolin makes our hands only white and dusty.
Talc is hydrophobic which means water-hating and hence it loves anything organic things. Kaolin, on the other hand, is hydrophilic. It makes it much easier to disperse into water than talc, which tends to sit on top of it. Talc may be water-hating but surprisingly, you can still disperse it into your water-based paint without too much of a problem. This water-hating property does come in useful in waterproofing products, where you need ingredients that help to reject water.
Kaolin is a clay mineral and falls into a family called alumino-silicates. Talc, however, is a magnesium silicate. This would explain their different behavior. However sometimes when you are just using them as inert fillers, their differences are not important and you would just buy whichever is cheapest – usually kaolin. Like when you are using them in laundry soap bars, for example. For white toilet soap, though, you will need whiteness, so then you would choose talc rather than kaolin.
It gets even more interesting when you melt these two minerals, as happens when they are used in ceramics. Kaolin is a basic ingredient of most ceramic bodies and glazes and is needed for its alumina content, while talc is used mainly as an additive which helps to control thermal expansion, reduce crazing and improve the whiteness of the ceramic article or glaze.