 Principles of Iridescence After quite a few years working with butterflies, I am still totally awe-struck at the crazily blue wings of the genus morpho. There is a simple (yet complex) reason why they are the blue they are – the colour is not down to pigment but to something else completely: ‘structural colour.’
Structural colouration was first observed by English scientists Robert Hooke and Isaac Newton in the 17th century, and its principle – wave interference – explained by Thomas Young a century later. Young described iridescence as the result of interference between reflections from two or more surfaces of thin films, combined with refraction as light enters and leaves such films. The geometry then determines that at certain angles, the light reflected from both surfaces interferes constructively, while at other angles, the light interferes destructively. Different colours therefore appear at different angles. Structural coloration is caused by interference effects rather than by pigments. Colours are produced when a material is scored with fine parallel lines, formed of one or more parallel thin layers, or otherwise composed of microstructures on the scale of the colour's wavelength; and so the combined action of interference and diffraction is essential for the structural colour of the Morpho butterfly. This photo of a morpho didius from my own collection is over a century old. It shows how perhaps structural colour weathers the rigours of time in a very different way to pigmented specimens… and I marvel at the glory of this blue 105 years later.  Pins, politics and patterns I've been reading a totally brilliant book about beetles and loved this wonderful insight.
Collecting insects (and of course everything else) has been part of our most primal natures, but it was only in the c18th that preserving and mounting specimens really became more possible, owing to a rather unlikely industry: pin-making. In 'The Wealth of the Nations', Adam Smith famously referred to pin-making as an example of efficiency that could be achieved by the division of labour, and by the the mid 1700s London, Gloucester and Bristol had become the largest pin-making centres of the world. Mostly used by the garment industry, pins were adopted quickly by the entomologists of the day as a way to attach their specimens. Up to this point, collectors had had varying degrees of success with maintaining their hoards - some even resorting to squashing specimens between the pages of a book. Good for flowers maybe but... It took a little while for mass-production of pins to allow for the manufacture of those made specifically for entomological use, but finally by the 1800s there was way to store, identify and arrange specimens more systematically. Those beautiful aesthetics around pinned specimens arranged in neat rows and patterns were born too. I love that early instructions from 1690 courtesy of one James Petiver (from his single folio sheet entitled: "Brief Directions for the Easie Making and Preserving Collections of all Natural Curiostities"), suggested that insects should be preserved by thrusting a pin through their body and sticking them to one's hat, until one has the opportunity to get a board and pin them to the wall of one's cabin, or the inside of a 'deal' box, so that would avoid being crushed. More soon (ish), T |
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