A really fascinating series of posts over at Tim Cullen's blog http://malagabay.wordpress.com/2013/10/27/liesegang-rings-1-the-liesegan… … which goes back to experimentation in the 19th century that resulted in the discovery of photography and television, creating pictures out of nowhere.
Raphael Liesegang was a German chemist and became fascinated by liesegang rings after discovering them while researching photographic emulsions. Frederic Runge had earlier stumbled on to them, calling them 'self painting pictures' and going so far as to write a book that never caught the imagination of the public – or of science. Lieseganag rings are observed in a lot of chemical systems undergoing a precipitation reaction – under certain conditions. Chemical patterning is now known as self organisation and Runge was ignored for some 40 years, until Liesegang was experimenting and accidentally dropped a small crystal of silver nitrate onto a chemical specimen and found it formed concentric rings. He went on to publish many papers on the subject (the field of spatio temporal precipitate patterns).
Liesegang rings are usually demonstrated using a gelling agent (such as gelatine) but they can also form in solid and gaseous chemical systems. It is essential to read the article and look at the images.
Tim Cullen notes, and here is where it all becomes interesting, there is clear evidence that indicates the liesegang phenomenon is not just a chemical process of periodic precipitation. Unfortunately, this additional evidence seems to be generally ignored, probably because it involves the heretical electromagnetic spectrum. For example, it has been observed that liesegang bands will appear after the gel has been exposed to sunlight. Secondly, there is evidence that the patterns can be regulated by an electric current so that information can be encoded into the precipitation patterns.
Liesegang rings can appear in nature in very different systems (bones, teeth, agate rock, bacterial colonies, alloys etc) – go to http://malagabay.wordpress.com/2013/10/31/liesegang-rings-4-biology/ … and Cullen says that atrributing 'real world' observations to the liesegang phenomenon became a somewhat arbitrary decision because there was no established scientific theory that comprehensively defined it. Patterns are found in nature – such as the stripes on a tiger or zebra, the patterns on the wings of a butterfly, and so on. Biologists attributed many patterns in nature to liesegang rings for close to one hundred years – without actual proof that they were due to the liesegang ring phenomenon. We may note that living body cells contain gel – which might be of biological significance.
Meanwhile, D'arcy Wentworth Thompson proposed something analogous to the liesegang phenomenon in order to produce animal markings – (see 'Shapes: natures patterns; A tapestry in Three Parts' Philip Ball:2001). As a result of the liberal use of liesegang rings, including lots of evidence of guesswork, the process became tainted, and it became just a matter of time before science found other ways to produce animal markings (see Alan Turing, 'The Chemical basis of Morphogenesis (1952). Alan Turing came up with the idea that animal coats, plant phyllotaxis, and chicken feathers, as an example, can spontaneously take on spotted, blotched, or striped patterns by a chemical signature and this changed the whole view of biological research, liesegang rings falling rapidly out of favour, as these things are wont to do. Cullen appears to think this was throwing the baby out with the bathwater as liesegang rings had suffered from too much conjecture and not enough research. He has a point. So do the modern biologists, it should be noted.
Turing's mathematics came to the fore in the later 20th century but Cullen claims it has never been experimentally proven – whereas liesegang rings were originally found in a laboratory experiment (by accident). He claims they can be seen in fungi and various organic forms such as moulds but the problem is the elusive factor that governs them (quoting from http://seedsaside.wordpress.com/2008/02/21/liesegang-rings/ and in medicine. Liesegang rings in inflammatory breast lesions, and balo concentric selerosis (a borderline form of multiple selerosis), are provided as examples (with illustrations). He then recommends reading Heinz K Hensch, 'Crystals in Gels and Liesegang Rings' (1998)