Lustrous or not?

A sorting challenge: collect small pieces of paper, cardboard, wood, chalk, copper wire, aluminium foil, and things made of brass, bronze or steel. Which ones shine when light falls on them? Look at their shine, texture and colour, and group them.

Materials with a shiny surface are lustrous: they have lustre. Lustrous materials are usually metals, such as iron, copper, zinc, aluminium and gold. Aluminium foil has lustre.

But some metals lose their lustre and look dull, because air and moisture act on them. That is why we often see a metal's lustre only on a freshly cut surface. The Statue of Liberty in America is made of copper; over the years it has lost its shine and turned green.

Materials without a shiny surface are non-lustrous: paper, wood, rubber and jute. A rubber eraser has no lustre.

An old saying: 'All that glitters is not gold.' Not everything that shines is a metal. A diamond sparkles but is not a metal. Some surfaces are made shiny by polishing them, or by coating them with a thin layer of plastic, wax or something else.