How can a surface be polished for some waves and not others?

[zachcumer]

[SOLVED] How can a surface be polished for some waves and not others?

The question is above...
Thanks

 

[mgb_phys]

A surface is always smoother (more polished) for a longer wavelength.
So a piece of wood is pretty smooth to 3cm microwaves but is not really lambda/20 for visible light!

 

[zachcumer]

thanks so much...I was thinking about writing just that but wasn't too sure.

thanks