Friday, September 10, 2010

Chemistry: Refractive index

All materials reflect and refract light, which is to say all materials alter the angle of light. The refractive index is a ratio defined as the speed of light in a vacuum (which equals 1) over the speed of light in the material. Light slows down when it enters a substance, so every refractive index will be over 1. The higher the refractive index, the higher the light intensity reflected from the surface. Titanium dioxide has a refractive index of 2.7, one of the highest of all materials, and diamonds are about 2.419 - and we know how sparkly they can be! - whereas water is around 1.33.

This term is really relevant in mineral make-up fillers because sometimes we want to reflect a lot of light and other times we want to absorb it so we don't emphasize those fine lines in our skin! If you are using micas, for instance, you have a lovely refraction rate that makes that glitter and shine we like. If you're using iron oxides, you won't get that same effect as the refractive index is quite low. Micronized mineral make-up fillers are less refractive than the non-micronized versions. The higher the micron size, the more reflective and shiny the filler will be.

And it's relevant in hair care products! If you want shine to your hair, you'll want to choose ingredients with higher refractive index levels. Dimethicone has a higher level than cyclomethicone, so adding more dimethicone to an anti-frizz spray will increase the shine on your hair!

1 comment:

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