Saturday, 20 August 2016

Caustics caustics!

On August 17th we made a trip to Trowbridge to discuss our project with Professor Sir Michael Berry, a physicist who specialises in caustics, the optical phenomena central to our project.

After meeting up with Michael, the day began with a session watching glassblowers at work; something I [Scott] had never seen first-hand, despite working with a glass artist for over a year. We spent an hour at the Devereux & Huskie Glassworks Studio — friends of Shelley’s — and watched them make a beautiful piece of layered blown glass. The process especially fascinated me for its materiality and intense performativity. The three artists worked together to keep the glass at the correct temperature for optimum malleability, and to keep several kilos of molten glass in constant and even rotation to stop it sliding off the blowing pipe. All of this while continuously shaping and pressing the glass into a unique and elegant form.

We also had some fun watching James and Katie make some ‘Prince Rupert’s Drops’ for Michael.
'Prince Rupert's Drop' or 'Dutch Tears'
After this we went for lunch with Michael to chat about our project, especially the nature of the caustic light phenomena, and their relationship to spectral behaviour in sound. 

Michael is Emeritus Professor of Physics at the University of Bristol. He specialises in the mathematics of light focussing, specifically caustics, phenomena that lie in the 'borderlands between physical theories — between classical and quantum, between rays and waves.' If you’d like the details, Michael’s website hosts his many papers that explain the complex maths behind these phenomena. However, for non-mathematicians, he describes caustics simply as the ‘spectacular patterns of wave interference associated with focusing’: common examples can be seen in the shimmering patterns of light on the bottom of swimming pools and clear streams. This older paper of Michael’s explains the phenomena very clearly, and here’s a beautiful example of a cusp caustic in very fine detail (from Michael's site), and a diagram of caustic formation (from paper cited above).

Talking with Michael changed the way we think about some of our project, or if that's too radical, the conversation at least provided us with another way of thinking about our materials. The primary point for me was that it's possible to generate caustics that are more 'pure' (see below) by removing the refractive aspect of the glass from the equation.  'Pure' here means an image that is only the caustic rays, avoiding multiplying of the image by glass refraction and internal reflections. This is not necessarily the best approach for the project goal of developing a visual grammar for a graphic score, but it certainly provides another aspect to that grammar, another voice. 

The simplest way to do this within our project is to use silvered glass, this allows us to reflect directly off the silver and allowing the curving of the glass to generate the caustic focussing. We can then also contrast that against caustics generated by shining light through the glass, wherein the cording of the glass multiplies and distorts the caustics. Both of these cases provide rich visuals with clearly identifiable elements

A second new element is to trying using laser light as well as white light. Our previous performances have used tightly focussed white light, which gave us good results, but seeing Michael's work with lasers has convinced us to try this approach as well. I've done some experiments using a simple laser pointer, with good results. The patterns from laser light are slightly different (apart from the very obvious difference that they're bright red...) but I haven't yet become familiar enough with them to properly define the different quality: watch this space... Here's an example:

As well as these direct impacts on the project, it was also fascinating to talk to Michael about aspects of chaos theory in his work, as this had a strong influence on my PhD work. I hope to have the chance to chat to him again as the project goes on.

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