Where does the white colour go when the snow melts? | Notes and Queries

Where does the white colour go when the snow melts?

Tim Hope, Norheimsund, Norway

• The colour we see as white is in fact the equal sum of all the colours in the spectrum. Snow appears white because it is a crystalline form of a colourless liquid (water). Although in microscopic close-up the crystals too are colourless, light is scattered from the crystal edges. Because this scattering is random, and all colours are scattered equally, the colours merge to give white light. When the snow melts, the light is no longer scattered in this way.

  Tim Waterfield, Montreal, Canada

• Nowhere: it is not a pigment. The whiteness is caused by the scattering of light by snow, firn and ice crystals. Liquid water does not scatter light to the same degree (unless frothed by turbulence), though it can refract light and show up green or blue parts of the visible spectrum.

  David Alexander, Amherst, Mass. USA

• It goes where the flame goes when your lighter runs on empty.

  Robert P van Driel, Antwerp, Belgium

• The snow is only white because of its complex structure - it reflects the light about rather than letting it pass straight through like water does. It's like when a pane of glass (such as a car windscreen) becomes fractured and gets criss-crosses of white lines through it where the cracks run. If you melted the glass, it would be clear again, as would the snow.

  Dan Norcott, Loughborough