Glass Bead Bow on Tarmac

When passing a cross-walk, a colourful bow is not what one expects to see there. So Jordan Stabile was very surprised when discovering the colourful bow on the tarmac in Somerville, Massachusetts, USA.

The answer to this problem is a rainbow, but with the difference that in this case the light is not reflected by drops of water, but by transparent spherical glass pellets. These have a diameter of about 0,25 millimetres and are used for sandblasting especially at cross-walks. As glass refracts light in a bigger angle than water does, the bow is smaller than a normal rainbow, with a diameter of only 20°.

A glass bead bow can easily be reproduced by placing a lamp over a sheet of black paper, on which glass beads (available for example in building supplies stores) have been spread before. Then a colourful bow (photo) appears on the paper. As the distance to our two eyes is very small in this case, the bow can also seem to float tridimensionally over the paper.

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