Iridescent colours

The modem era of biochemistry and molecular biology has been shaped not least by the isolation and characterization of individual molecules. Recently, however, more and more polyfunctional macromolecular complexes are being discovered, including nonrandomly codistributed membrane-bound proteins [41], These are made up of several individual proteins, which can assemble spontaneously, possibly in the presence of a lipid membrane or an element of the cytoskeleton [42] which are themselves supramolecular complexes. Some of these complexes, e.g. snail haemocyanin [4o], are merely assembled from a very large number of identical subunits vimses are much larger and more elaborate and we are still some way from understanding the processes controlling the assembly of the wonderfully intricate and beautiful stmctures responsible for the iridescent colours of butterflies and moths [44]. 

Tyndall scattering also causes the blinding effect of shining a car headlight directly into a thick bank of fog or mist it also yields the beautiful iridescent colours on the wing of a butterfly or peacock tail, and an opal and mother of pearl. A good potter can reproduce some of these optical effects with so-called iridescent glazes, which comprise colloidal materials. 

Colour variable pigments in our Variocrom range are made of pi-large aluminium flakes which are covered by several layers of Si02 and Fe203, each a few hundred nanometers thick. This multi-layer plate-like structure produces an angle dependent, iridescent colour play. The Si02-layer with a... 

The pearlescent effect in natural pearls arises because of the interaction of incident light with alternating layers of high refractive index (CaCOj) and low refractive index (protein), reflected and diffracted light from which leads to the observed iridescent colours. 

Rapid cycling through iridescent colours - Peacock s Tail. 

Figure 15.6 (a) an opal bracelet and (b) the iridescent colours of the Madagascan sunset moth. The... 

Cholesteric and nematic liquid crystals can exhibit very large optical activities cholesteric types often exhibit iridescent colours due to dichroism. 

To form helicoids, each individual nano-fibril is arranged parallel to another one in stacked planes. From plane to plane, the orientation of the fibrils changes by a few degrees to obtain the helicoidal structure. While in many instances the dimensions of such helicoidal structures are not on the right length-scale to produce structural colour, there are many examples where such hierarchical structures provide a vivid and strong iridescent colouration. 

The adoption of a particular metalfinishing treatment is often sensitive to fashion as well as technical and economic constraints. An example of this is provided by the recent introduction of anodized titanium jewellery, where the wide range of iridescent colours (dependent upon voltage and thickness) provide an aesthetically pleasing and durable item. 

All chromate conversion coatings use chromic acid in the form of its soluble salts. During the process, a thin, gel-like film is produced on the aluminium surface. The films produced by this process vary in colour, depending on the aluminium alloy being treated, surface conditions and the type of chromate. Chromate conversion coating leaves no measurable build-up on the component(s) and provides excellent corrosion resistance. The coating is conductive and offers in yellow iridescent to clear iridescent colouring. Electrical resistance increases with the darkness of the yellow colour. 

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