Why Are Most Metals Shiny Gray? (But Not All)
80% of chemical elements are metals. Most metals are lustrous gray when polished, but there are some exceptions, such as gold and copper, or less-known silvery-blue osmium, pale gold cesium, etc. The short answer to why it is so — is that the color of an object depends on its reflectivity. Reflectivity says how well a given object absorbs photons of given frequencies. Metals usually appear shiny because they reflect the light of all visible frequencies, while for colored metals, there is a certain threshold above which reflectivity drops.
This is why copper, which drastically stops reflecting in the orange part of the visible spectrum, has its characteristic reddish color. Similarly, the reflectivity of gold drops on slightly lower wavelengths (higher frequencies).
So, what is different about some noble metals that result in a drop in reflectivity already in a visible spectrum, earlier than it happens for other metals?
