I’ve always wondered how a really opaque non reflective material becomes quite glossy and reflective with just really smooth sanding?
Like paint, as I buff it, it becomes real shiny and smooth, and reflective. Even wood when sanding up to 5000 grit or higher!
In:
The smoother a surface is the less diffrence there is in reflection of light. Its the same thing when you take a standard sheet of steel and grind/buff it down to be extremely smooth. Youll have almost a mirror because most of the light is now reflected in a uniform manner.
There are two ways light can bounce off a surface; like a mirror (specular) or like a wall / wood (diffuse). We’re talking about photons and molecules which makes this quite tricky to wrap your head around, so lets make it bigger, we can imagine one of those tennis ball firing machines pointing at a smooth wall. If you fix the angle of the machine and just move it around the wall, all the balls will fly in parallel at the wall and, importantly, will bounce off the wall in parallel too. This is a lot like the ‘specular’ mirror reflection. Now, lets make the wall all lumpy bumpy. Whereas before the angle the balls made with the wall was fixed, now each ball will hit on different parts of the bump, so will bounce off in all directions – this is diffuse reflection.
So now we can go back to the microscopic case – when the light hits a smooth mirror all the reflections are ordered – parallel incoming beams leave the mirror in parallel too, so you can see an image. When the surface is bumpy the light get scattered in all directions. Hopefully now you can see that as you polish the surface, removing those bumps, the reflection will get less diffuse and more specular.
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