I started thinking about this in a discussion in comments.
One can start by thinking of the reflection of visible light by most metals as similar to the reflection of radio waves in that it's an interaction between an electromagnetic wave and an infinite half-plane of dense electron plasma. So long as the frequency is somewhat below the plasma frequency, this is a good starting point. Once in a while there are strong, obvious atomic effects such as gold metal being gold in color but many/most crystalline, amorphous and molten metals have high specular reflectivity and little obvious spectral variation, i.e. most of them look more or less "silvery".
Are there any crystallographic effects in the specular reflection from smooth metal surfaces that are visibly detectable either by looking at a reflection, or doing a simple experiment without an ellipsometer or other special equipment? Perhaps a simple polarizer film or plastic diffraction grating or something around a school science lab or home?
A visible "crystallographic effects" might be for example a difference in appearance or easy-to-observe optical behavior between
- two polished faces of a metal crystal having different crystallographic orientations,
- two polished faces of two metal samples of different crystallographic grain size, or one being totally amorphous
- a polished face of a metal crystal and the surface of the metal liquid at nearly the same temperature.
or it could be something visible that "happens" at a certain angle or under a certain condition or color of illumination for one sample but not another.