When light meets a surface, some will be reflected, but the remainder will pass below the surface where, either it is absorbed and the object is said to be opaque, or it passes through the object, which is said to be transparent or translucent. The speed of light varies with the medium through which it is passing and its speed through a transparent object will be slower than its speed through air.

The effect of this is that the path of the light is 'bent' at each boundary between the object and the air, (put a straight stick into water and it appears to have bent at the water surface), and this bending is called refraction.

The amount of refraction at the boundary is expressed by the refractive index.

                                        Speed of Light in Air

Refractive Index  =  ------------------------------------------

                                       Speed of Light in Medium

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The refractive index of Water is 1.33; Diamond 2.42. Titanium Dioxide has a higher refractive index than any other transparent material at 2.76.

Thus, by using Titanium Dioxide which may be transparent in solid form when it is finely divided and mixed with a resin of different refractive index the path of light refraction by the particles can bend the light sufficiently that the white light entering is seen as white light by the eye.

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