Of butterfly wings and that light feeling

I would not be the first person to find butterflies beautiful creatures with their gorgeous, coloured wings. What makes their lovely colours even more special is how they come about.

The beautiful Morpho butterfly exhibits a brilliant blue colour that is lustrous, is not affected by chemical change, lasts more than 100 years (can be seen even in fossils) and maintains its hue over a very large angular viewing range.

This colour arises not from pigmentation but from the structure of the delicate wings.
The wings have arrays of shelves that contain ridges. The interferance within a single shelf gives the blue colour while the diffraction of light from these ridges causes the wide angular spread over which the colour remains blue to the viewer. There is a degree of randomness in the shelves and which prevents other colours from being reflected by interferance. As the shelves are densely packed the reflectivity is quite high.

So what is interesting is that initially people thought that interferance from multiple layers gave rise to the specific colour(s) that we observe in insects such as Morpho. But interferance is by its very nature yields narrow fringes. Yet we observe the blue colour over a broad (angular) range and no fringes, a mostly smooth pattern. So much research has gone into explaining the nature of this colour.

What is amazing is that a wing that looks so delicate and thin can have such a complex structure on it!

Perhaps even more amazing is this way of creating colour. A method that gives fade proof colour that wont wash away, or lose it shine and will last a very long time and which is ecologically friendly!


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