Friday, 28 July 2017

Back to their future


It was about two years ago when my enthusiasm for very amateur astronomy got me into trouble (of sorts). Not that I knew it at the time, one often doesn’t. Hindsight is 20:20 they say.
A 360º time-lapse movie of the sky over Blean (north Kent, UK) taken with the skycam at the Beacon Observatory at the University of Kent. The mast on the right is the observatory’s weather station. Despite the local light pollution, it’s possible to make out several constellations as well as the Milky Way (– our Earth-bound view of our own Galaxy; in September, when this sequence was captured, the galactic centre would have been just out of shot). Read on to see how this fits into the post.
I can’t remember a time when the night sky didn’t fascinated me; in some ways one might say that it was my entry point into science. Had it been a subject available at my school I would have chosen it. As it was I had to wait until I was allowed to drive my parents’ car from our village to the nearest large town – in which there was a library running adult education classes in observational astronomy. I’ll never forget the first time, using my small [1] and necessarily inexpensive telescope, I saw the shadows of mountains on the Moon, the phases of Venus, ‘bulges’ on the side of Saturn created by its unresolved rings, and watched the motion of the four Galilean moon of Jupiter. There’s no going back after that. I even tried my hand at astrophotography: in classic ‘Heath-Robinson’ style – a ‘bricolage’ as they might say in France – I built a frame from scraps of wood to hold the telescope and my soviet-made 35 mm camera atop a tripod. It never did work; I couldn’t get the focal distances right. As the years passed by I spent less and less time outside gazing upwards: there were so many other things to focus on. The underlying fascination, however, never went away; more recently it has begun to re-surface – hence this post.
By the age of 13 I was using a notebook to make sketches and describe what I observed – here, what I later learnt were haloes around the Moon caused by high-altitude ice crystals.
A few months before my ‘retirement’ I was given on loan a somewhat larger and more sophisticated telescope [2]. It had been donated to a primary school, where no-one knew how to use it or had the time to find out, and for which no-one could foresee a practicable use given the young age of the pupils. The whole thing had just been re-discovered in a series of boxes in a cupboard somewhere. The idea was that I figure out how to run it and begin to explore what the school might do with it in the longer term. I’m still a long way from completing my task, but I have slowly mastered the basics. It’s too cumbersome to transport it away from my built-up and excessively illuminated neighbourhood, so I rely on the few shadowy spots on my front drive and rear garden for observing sites – and rejoice on those rare occasions when the nearest street lights fail. Thus, the motivation to set it up more fully each time it emerges from my garage is not strong. That notwithstanding, I am beginning to have a lot of fun with it. There’s an inexhaustible list of things to look at, and key goals remaining like viewing our near-neighbour galaxy, Andromeda. However, for now it remains a work in progress, and moves forward at the rate I wish to lose sleep on clear nights. 
My early attempts at photographing what I was looking at using my smartphone were far from impressive, although it was just about doable. However, things have begun to improve considerably now that I have invested in a simple clamp that attaches to the telescope’s eyepiece and holds the ‘phone in place. On the left is, self-evidently, my image of the Moon taken using a green filter; the crater rims near the day/night terminator when the Sun is low in the lunar sky are picked out quite nicely. (With a bit of trigonometry, the shadows provide a means of estimating the height of the mountain ranges; e.g. here.) Jupiter has been easily visible in the months leading to this post as the central image, taken directly using my ‘phone, attests. However, train the telescope onto it and the spot becomes a disk and the four so-called Galilean moons may be seen. I need to go back to this and try again with a suitable colour filter: the moons won’t then be seen, but the equatorial rings on Jupiter – gloriously visible with the eye through the telescope – might emerge in an image.

Now we reach the ‘indiscretion’ with which I began. On a return visit to my old department a colleague, Dirk Froebrich, an extremely talented astronomer/astrophysicist with an interest in star formation, reminded me that I had once asked if I could use the telescope [3] then being installed and commissioned on the edge of campus. He gave me the opportunity of being trained in its operation so that I might help to run their science programme when the core team were unavailable. Apparently, there was a period in June when that situation would arise due to conferences, holidays and trips to use really seriously impressive international observatories (e.g. here). I had no real conception of what I was letting myself in for, but said “yes please” nonetheless.
The telescope and its dome at the time I first volunteered. In the few months since then some additional equipment has been installed.
Apart from anything else, I was attracted by the thought that this would form a part of their ‘citizen science’ programme: school groups, amateur astronomy clubs [4] and their like could enlist to look through the data being collected and thereby perhaps contribute to new discoveries. It sounded genuinely exciting, and still does. The essence of the project, as I understand it in my amateurish way, is to measure the light coming from young stars in some of the star-forming regions of our galaxy. Their timeline starts with the emergence of higher density regions within one of the huge dust/gas clouds that exist; this might have been initiated by the effects of light from nearby stars perhaps. Slowly, these swirling masses begin to pull themselves together under the effect of their own gravity until each has a dense central region surrounded by more dust/gas which is attracted inwards under gravity. Each of these entities is rotating: faster now, because that’s what happens when the diameter decreases – think of an ice skater speeding up as their arms are drawn in to their body. Eventually, the central region may become massive and dense enough for nuclear fusion to begin; a star is born. If smaller regions begin to coalesce in the surrounding disk of dust, its accretion disk, then we may see the development of planets, asteroids etc. Unless, that is, the outward pressure of the light and other emissions from this new star overcomes its gravitational attraction and thereby ‘blows’ the dust away. (There’s quite a narrow window, cosmologically speaking, for planetary formation to begin it seems: unless it’s underway within a few millions years the star will indeed blow the dust in its accretion disk away into the
surrounding galaxy. I have adapted an artist’s impression, shown here.) Now, our young stars don’t collect additional matter from the surrounding disk at a uniform rate it seems. A given star may have periods when its brightness increases quite significantly because the rate at which it is accreting new matter from the surrounding disk has increased markedly. There are theoretical models for all this, but a lack of data. This is where the citizen science project comes in. Light curves are very carefully measured and those measurements repeated over an extended period – every cloud-free night for which they are above the horizon in fact – and a hoped-for army of interested volunteers seek out the tell-tale signs of a sudden change in brightness.

I spent most of a night having the necessary software loaded onto my laptop and taking copious notes as I watched over Dirk’s expert shoulders, and another night with him carefully watching me, driving-instructor-like. Then came the fearful part: running the show myself from my laptop at home. I spent my professional life as a scientist using very expensive, often unique, pieces of equipment in pursuit of new knowledge (e.g. in this earlier post). But, perhaps because this is not my area of expertise or experience, finding myself in sole charge of this £100,000+ observatory for a night felt peculiarly daunting - indeed, downright stressful. Thankully, in the short intervening period I have made mistakes, but damaged nothing. Despite what some might consider the foolishness of actually volunteering to lose sleep, I have continued to learn, which is of course what I wanted to do (- alongside making a positive contribution).
There are a lot of windows to monitor, so I connected my small laptop to my home PC’s screen. On a second, older laptop I had radar images showing cloud-cover over my part of the country – that way I had at least an hour’s warning of approaching poor weather, which gave me time safely to close everything up.
‘The proof of the pudding is in the eating’ as the old saying has it. Shown below are the four images associated with my first full night of observation. They are VRI (i.e. individual colour filtered images, later combined) composites of IC1396A, IC5070, MWSC3274 and NGC7129, about 15min integration in each filter. Each is a region of the nearby galaxy in which star formation is occurring; the dust/gas clouds are clearly visible (e.g. top left). The most distant region is approximately 3300 light years away; we’re therefore photographing and measuring it as it was when Tutankhamen died, the first books were being produced in China and a little before the time of Moses. I was looking back in time from a vantage point which may represent their future.



Footnotes:
[1] A refractor with an aperture of about 30 mm at a guess.
[2] A 102 mm, Maksutov-Cassegrain reflector on a motorised equatorial mount, along with an impressive selection of eyepieces and filters.
[3] This is a beautiful beast: a computer-driven reflector with a mirror aperture of 432 mm (i.e. almost 20 times the mirror area of my borrowed telescope, and of far higher optical quality) and with a 16M pixel cooled CCD camera; further details here. The whole thing sits elegantly within its bespoke observatory dome (also driven remotely via computer), together with its own weather station etc.
[4] Perhaps like the club I visited recently, Ashford Astronomical Society: lovely people, full of enthusiasm and experience – highly recommended. I was invited by a graduate of my old department, Emma, who is a leading member there; she and her husband were jointly, and expertly, giving that evening’s talk.



Saturday, 22 July 2017

Radiation in my living room



The University of the Third Age, U3A, was one of several positive discoveries made after I ‘retired’ as an academic and research scientist. It has, for instance, given me the opportunity finally to indulge in more creative writing – within a small group in which, comfortingly, I’m not the only person with a STEM* background. Some of the early-stage output from this endeavour is featured in a previous post (here). The other ongoing need in my life transcends the move from salaried employment to ‘going freelance’: trying to communicate science and my love for it to lay audiences. Although I’d been doing as much of this as I could fit in prior to retirement (e.g. see here or here or in umpteen other posts on this blog) and ad hoc invitations to do this have continued, I felt the need to go beyond one-off short talks. Again, the local branch of the U3A has provided a useful framework. And so it was that, last Autumn – my first year as a member – I opened my living room to a small group of brave souls who’d each paid £3 per session (to the U3A) in order to hear a complete stranger talk about glass. I had three two-hour sessions scheduled, so plenty of scope for peppering the science into a swathe of images and artefacts, art and history. The feedback was really positive, and word evidently spread that there’s more to glass than meets the eye (!) because my re-run of the course this coming autumn has far outgrown my living room and we are being moved to a larger venue in the city. This is hugely gratifying, but more importantly it helped to persuade me that my approach to presenting science in this context was broadly OK. However, talking about glass is, for me, an ‘easy’ thing – it can be harder to stop. I set myself a new challenge.
The opening slide: ready to welcome my brave audience.
One of the things I perhaps ought to take on, or so I told myself, perhaps naïvely, is the use of my training and experience in trying to demystify potentially more contentious aspects of the physical sciences … like radiation for example. It’s a topic I’d introduced to many Physics students over the years, so I had a bit of material to work with. However, the more I thought about it the more of that material I discarded. What was needed, I reasoned, was about an hour’s worth of material which I could spread over 90+ minutes to allow for questions and audience-led detours. The material needed to address the basic requirements of explaining just enough of the science and the terminology for everyone then to make sense of my attempt to introduce a more open-minded perspective than one often sees in the media. In the end I spent goodness knows how many hours researching and preparing new material that I thought might better do the job. In all this it was important to keep the talk grounded in contexts that one might readily appreciate: medical uses of radiation, radiation from the ground below and the sky above, nuclear power and the accidents we’d all have heard about, and so on. Part of this grounding required that we did more than stare at slides; thankfully, I have a Geiger counter on loan from my old department and managed to borrow a set of radioactive minerals from its hugely successful schools outreach team (here, run by a wonderful ex PhD student in my former research group); that would get us started.

The U3A run an annual series of ‘Summer Specials’: essentially taster sessions prior to members selecting what they might like to register for in the main programme, which starts each year in the Autumn. They also allow one to try out ideas for possible new courses, and this therefore provided an ideal vehicle for me. This is what I proposed:
Radiation: beneficial, benign and bad
Radiation, in its many guises, has been a ‘hot topic’ for more than 70 years and a matter of considerable interest of over a century – but how much do we know about it? In this taster session, we’ll take a look at its origins and effects – beneficial, benign and bad – from a scientific perspective. There ought to be no need for a formal science background beyond school-level, and questions will always be welcomed should you need to brush up on something. There will be a little radioactive material used within the session, but nothing that will represent a safety concern for any of us.
The registration list filled within a day or two, and a list of reserves began to form. There is evidently an appetite for such topics; so far, so good.

In the event, I found I had more than enough material for an hour’s worth of my talking. This was a good thing in the sense that it allowed all the space required for what turned out to be a large number of challenging, high-quality questions that emerged as we went through. The downside is that we had less time for connected discussion at the end, but addressing the questions as they arose was definitely of more importance. Indeed, for me, getting good questions is one of the best forms of immediate feedback.
What did we cover in the end?
After introducing ourselves and grabbing a drink and a biscuit or two, we spent a few minutes on the 92 naturally occurring elements and their 1000+ isotopes, and in establishing the prevalence of radioactive isotopes in particular. Next, an overview of the principal forms of ionising radiation and how one might tell which is which; then, how they can be detected using a Geiger counter, and what sort of units we measure them in (the Becquerel, Bq, and the Seivert, Sv, in our case). The final bit of scientific background covered the meaning of the half-life as well as illustrating the concept of the decay chain. No equations saw the light of day – reflecting an important lesson I learned long ago. All-in-all, with questions, we spent about half our time on the basic science before moving on to consider the bad, the benign and the beneficial.
I chose to reverse the order of the aspects of radiation drafted into my purposefully tantalising title: ‘bad’ is, in a very real sense, the easiest to cover – it is, well … bad.
‘Benign’ became, in practice, ‘unavoidable’: we looked at radiation coming from beneath our feet, e.g. from the granite beneath much of the UK’s West Country, and from space; we went on consider the raised levels experienced when flying and then to think through the consequences of the phrase “we are what we eat” in terms of radioactivity within our bodies. This was a good point at which to fire up the Geiger counter to get a sense of the natural background and to examine my borrowed collection of minerals. (The latter came with a thin sheet of lead in a plastic bag and the lid from a tin can – very useful tools in determining what sort of radiation our small lumps of rock were emitting.)
Our final topic came under the heading of ‘beneficial’, and here we looked at medical diagnostics and radiotherapy, at the formation of helium as a product of radioactive decay events within the Earth and at useful aspects of radioactivity such as carbon-14 dating within archaeology. We also considered the nett benefit of having radioactive events within the Earth since they help to heat the interior of the planet and thereby maintain our molten core: without this we’d not have a magnetic field to shield us from the solar wind, and we’d then suffer far, far more radiation from the Sun.

As I’ve said already, a constant theme was always to think in terms of perspective – the balance of risks. I wanted us to leave the session with an appreciation of what radiation is, where it originates, how much of it we encounter and what it does. My hope was/is that the group would thereby be better equipped – one might even say empowered – to engage with current and future debates. Reactions on the day exceeded all my expectations, and what people have kindly said in various emails since then has been truly humbling. One person made a very positive suggestion for improvement which I’ll definitely adopt. I doubt I shall ever forget the two people who, quite separately, said that had they been taught science like that when they were at school their later choices might have been very different. It doesn’t get much better than that.
My parting slide, philosophically tongue-in-cheek, is shown here. We could have spent an entire session exploring these three points alone – and perhaps one day we shall – but we ended our two hours together with the suggestion that they be mulled over. As it turned out, I was motivated to post a brief reflection on the middle one in the week after my U3A talk: here, should you wish to read it.

* STEM – Science, Technology, Engineering and Mathematics; sometimes an additional ‘M’ is added in order to include the Medical sciences.



Wednesday, 12 July 2017

“Science is always wrong”


All the while I was doing it I would get quizzical, sometimes incredulous looks and comments from a sizable fraction of my academic colleagues. Why, they would ask, do I fight to stay closely involved when, in my position – whatever that was I never did fully understand, I could take my pick? ‘They needed my experience elsewhere’ where I would, apparently, ‘get a better shot at picking up research students’ … and so on and so forth. It wasn’t that dissimilar to the internationally well-known and highly respected senior colleague at a previous place of work informing me that I must be mad to leave a fast-track* career there for a junior academic post at an obscure provincial university. Their snippets of advice weren’t a million miles away from so many others I had heard before and have politely listened to since, all of which I am prepared to believe were well-meaning, and many of which may even have been right. However, sometimes no amount of dissuasion will ever be enough.

I helped to design our Foundation Year in Physics (which currently looks like this). It was a time of weak student recruitment and there’s no doubt that this motivated my head of department’s decision to task me and a couple of colleagues with the job. School-leavers with the ‘wrong’ qualifications to enter a Physics degree by conventional routes might change direction or make up for past under-performance by taking what was, in essence, a pre-degree programme of study. Result: more students going into Year 1 of our mainstream undergraduate course. Despite an initially reluctant involvement, I soon came to recognise that this had the potential to offer a ‘second chance’ to people who might need it. Goodness knows I’ve benefited from many of those in my time. Through more than two decades between its formation and my retirement, typically teaching over a quarter of the course to cohorts of up to 70 in number, I never found a group of students more worthy of my investment than were these ‘Year 0’ students. It is no surprise then that most of the innovations I experimented with were introduced in the hope of benefiting them – and thereafter the other groups I taught; I wrote about some of this in a couple of earlier post, here and here. What does this have to do with the title (which, by the way, is extracted from a longer quotation by George Bernard Shaw, see here)?
Read on …

One of the challenges was to persuade students who might regard themselves as ‘failures’ in one sense or another that they had something to contribute. An excellent route turned out to be the use of film/TV/computer game clips and other mass-media as a way into discussing their respective physics content, but another was for me to light a fuse by making an ostensibly outrageous comment – like the one in my title – and watching them defend their chosen subject. Eventually, we’d meander to the point at which most would recognise the kernel of truth in the proposition: history tells us that science is indeed always ‘wrong’. Let’s take one obvious example: the intellectual giant Isaac Newton gave us many elegant descriptions of the physical universe around us and no school textbook on physics is complete without the equations derived from his work. His research on light and colour, for instance, out-lasted the other descriptions available and still holds sway (see my post here to learn more). His description of the effects of gravity, although supreme for more than three centuries and still quite effective in most everyday circumstances, eventually gave way to Einstein’s work on the General Theory of Relativity. In other words, put crudely, Newton and the science associated with him was proved wrong in this regard. ‘Science’ was wrong and needed to be revised. The scientific knowledge we have today will be in need of revision tomorrow. It’s a humbling thought for us scientists – and we fail to take it on board at our peril. There is however a postscript to this line of reasoning. Whilst the results of scientific endeavour are always subject to change over time, it remains the case that that they give us the best insight into the workings of the physical world that we have at a given stage of history. We would have been fools to ignore Newton’s work, and thereby miss all the opportunities for advancement it afford us, on the off-chance that an Einstein was around the corner. We need also to keep in mind that science is more than its results: it’s a methodology, a way of asking questions and testing the limits to our understanding of the material world that is less susceptible to the vagaries of the human mind than some other means of inquiry.

My own early-stage career, as a graduate PhD student in the 1970s, put me in the position of demonstrating that one set of theories was inadequate and that an alternate was required. It was a scary thing to do at the time. Analogous thresholds have been crossed by the excellent former members of my research team from the mid-‘80s onward. However, there is only one true test of the commitment of an individual scientist to the principle of humility outlined above: what happens when one of their own pet theories or shiny experimental results are shown to be in need of revision … or replacement.

Now we reach the impetus behind my drafting of this post. A few days ago I received an email from a member of a German-Canadian research team describing in some detail why their recent data might require that a piece of work I was involved with over two decades ago probably needs to be re-interpreted. The email to me was a kindness – they could simply have written to the editor of the appropriate scientific journal and immediately lodged their comment in print; they wanted instead to see whether, on behalf of my co-authors of the time, I might like to say something first. I wrote back immediately. I shared with them the impracticality of pulling together the people and raw data of more than 20 years ago to undertake a re-analysis in light of this new information. I’m also pleased that I can say that I was able to commend and thank them for their work; I reassured them I saw this as science gaining benefit from their careful review.

Phew:
https://goo.gl/images/5N7Juf

* His words, not mine: I was never ‘fast-tracked’ through anything as far as I am aware, nor would I wish to be.



Friday, 26 May 2017

Paintings in Light



Welcome to the second instalment of my two-part post on the interaction of light with glass. The first part (in which I attempted to cover some foundations regarding what glass is, its transparency, the way light behaves as it passes through and how one can introduce colours) may be found here. As promised in that initial post, the intention is to move on to stained glass windows, and to highlight the interdisciplinary work of conservators who are committed to passing on these inherited treasures to future generations. Before diving into the subject itself I must acknowledge several people. First, my friend Martyn Barr who generously allowed me to recycle the title of his excellent book and use it as my own (see here, second and third paragraph, or here for further details). However, absolutely central to this piece is Léonie Seliger and her wonderful team at the Glass Studios of Canterbury Cathedral; I never tire of visiting them and of being able continually to learn new things from them. I am also very grateful to Jane Walker, the Cathedral’s Head of Communications, for her permission to use the images I captured on my 'phone during a recent visit.
Before I focus on the glass of Canterbury Cathedral I’ll share with you a few images from elsewhere, ecclesiastical and otherwise. On the left is a window I photographed in Folkestone (Kent, UK; All Souls church) after delivering a talk on glass there: the window was donated by the artist, Gabriel Loire, in the year of my birth; it is made from ‘chunks’ of coloured glass rather than cut sheets. Middle top shows a small part of the Roots of Knowledge windows by Tom Holdman, with the Big Bang depicted on the left and prehistoric humans to the right. Below that is shown a stained glass garden sculpture by Joe Szabo, spotted during a visit to the Royal Horticultural Society’s Wisley site. On the right are two examples of Louis Comfort Tiffany’s work; the top one I was fortunate to see during a visit to Chicago but not, sadly, the collection of lampshades shown below .

I doubt there are many people who are unaware of stained glass, even if they’ve seen only images; there are windows and other works of art based on the use of coloured and painted glass in buildings right around the world. In Europe, the techniques employed to create them date back more than a millennium, and novel examples continue to emerge. In order to maintain focus and to avoid turning this into an overly-long post, I will not attempt to describe how a window is made; that job has been done many times over (e.g. in Martyn Barr’s highly accessible book, see above, and in videos like this one, and this). The essential stages begin with the artist’s design, then cutting and shaping appropriately coloured glass to that design before painting on the fine detail – which may be fused into the glass surface using a furnace or occasionally ‘cold-painted’ onto the glass. The individual pieces are slotted into place using lengths of ‘H-shaped’ lead which are soldered together at each junction. For a large window comprising multiple sub-sections of the overall design each part is then tied to a supporting frame, usually of iron, using copper wire which has been soldered to the lead. There are variants on this formula, as in the windows created from relatively thick ‘chunks’ of coloured glass broken from a large block to create a more abstract effect, but I’ll confine my coverage of those to one of the images above.
These images will hopefully illustrate the way in which glass pieces are assembled and then sub-sections of a window are fixed to the frame. Copper wire is first attached to the leading, as in the mock-up shown top right, before being twisted around the frame to support the assembly in its final resting place. The ties shown in use on the right help to support Canterbury Cathedral’s Great South Window, recently re-installed after the surrounding masonry was replaced/renovated and the glass disassembled for conservation work. The image on the left shows the scaffolding I climbed through – with permission and a hard-hat, naturally – in order to get the in situ image.

When light passes through them, the windows ‘come to life’. However, the way in which they do so is affected by more than just the nature of the incident sunlight. For instance, in glass sheets made by traditional methods rather than by the commercially dominant float glass process – blowing a tube shape, cutting off the ends, slicing along its length and allowing the cylinder to fold outwards – there will be variations in thickness apart from anything else. Add to that the fact that older glasses, medieval for example, will probably include cullet (waste or recycled glass) of varying provenance, and differences in colour/shading from one part of the sheet to another will almost certainly be apparent. The fragment shown here illustrates this effect. There is a great deal of fascinating
archaeological science undertaken on such specimens, and the origins of particular glasses may now be revealed in some detail by studying the material at a microscopic level. (For those wanting to dig a little deeper, into the red-coloured glasses of antiquity for example, I suggest a close look at the accounts published by Ian Freestone, who is also very much involved in the project I initially outline here (second half), and which I’ll update below.)

One of the more profound effects of a stained glass window on the light passing through it, beyond selecting out a particular colour that is, is associated with the phenomenon of light scattering. Whether we realise it or not, we have all seen the effects of light scattering: blue daytime skies giving way to red sunsets, the whiteness of clouds and of milk etc.; all of this is due to the way in which particles (dust, water droplets, suspended fat droplets etc.) scatter beams of light. So it is too with stained glass windows. If through the effects of corrosion or by the artist’s will the surface regions of a piece of glass become porous, or perhaps picks up a ‘powdery’ layer through chemical attack or the accretion of particulates, something similar happens. Viewing such a window from the inside, that is to say with the window back-lit, gives the impression that the window ‘glows’ – the light coming through it is being scattered in all directions, irrespective of the colour of the glass. This is beautifully illustrated in the images below, associated with a major exhibition mounted by Canterbury Cathedral’s Glass Studio in the USA (see here and here). Some of the oldest surviving medieval stained glass windows that were being removed as part of the Cathedral’s rolling programme of building conservation work travelled to the USA for a season, and as a part of the exhibition the Glass Studio team made a modern replica of one of those windows …
Look first at the image on the left: which window comprises old, ‘rough-surfaced’ glass and which is the modern replica? Both are identically back-lit. Notice that the window on the left looks relatively ‘dull’ yet casts a bright pattern on the floor, whereas the window to the right of the picture appears much brighter but casts only a shadow on the floor. This illustrates the effect of light scattering. The modern window is on the left: the light that passes through it simply travels on until it reaches a surface, in this case the floor. The original window on the right of the picture takes the light that has passed through the coloured glass and, at or near the surface, scatters it widely – so we enjoy the coloured glow from whichever direction we view it, but very little of that light is left to carry on through to the floor. The photo on the right shows the head of the Glass Studio, Léonie, and a senior member of the team, Laura, standing in the transmitted light of a large modern window: just think of the patterns of brightly coloured light that would have bathed Canterbury Cathedral when its medieval windows were young.
Now we move into the realms of conservation. One might naïvely suggest any surface layers ought to be cleaned off in order to return the glass to its original state, but nothing is that straightforward. Remember that some surfaces may have had detail added via the application of a paint, which may have been fused into the surface or simply be applied ‘cold’. Moreover, many of the older glass pieces may be fragile and there is a risk of irreparable damage – especially if the surface layer turns out to be deeper than anticipated. Then comes the need to know what the surface layer is made of since whatever is used to remove it must not also damage the native glass below; this itself can be a complex issue to resolve. However, the question becomes far more complex when the glass artists themselves apply a surface coating since current thinking is that an intentionally applied layer must be left in situ – irrespective of whether we might feel it was ill-advised, or whether it has changed over time. After all, many world-famous paintings change over time because their pigments or other media were not stable – this can be a serious problem with some of the J.M.W. Turner’s work for example because he was keen to experiment with novel paints – and we would be outraged if they were ‘tampered with’. In terms of stained glass windows this particular issue is widespread. For instance, it was not uncommon for Victorian (i.e. 19th century) stained glass artists to try to make their windows look older than they were: perhaps by sprinkling iron fillings onto the surface and then fusing them into the glass in a furnace. Ironically, this has in some cases left us with medieval windows that appear to be younger than Victorian ones. Adding a colour-wash to the surface was also practiced, perhaps to reduce the brightness of a particular section in order to keep it more in line with the window as a whole or artificially to generate the light scattering effect discussed above.

It is exactly this sort of issue currently facing the Glass Studio at Canterbury Cathedral: Victorian windows that are being removed as part of their wider conservation/renovation programme and which, to use the technical term, have a series of ‘blobs’ or patches in particular locations on the glass. The problem was outlined in a post I uploaded last year: here, second half. However, the good news with which I will end this update is that a strong international team of experts is now pooling its efforts in order to resolve the problem. Thus, added to the considerable experience and expertise of the staff of the Glass Studio is an archaeologist from University College London, Ian Freestone, who specialises in applying scientific methods to the study of old glass, and a conservation scientist from Lisbon, Márcia Vilarigues with a wealth of relevant knowledge. I met Ian a few years ago, and have been reading his papers for much longer, and had the pleasure of meeting Márcia for the first time at the conference on glass I wrote about in the post mentioned just above. We finally managed to get us all together a few weeks ago and spent the best part of a day touring the site and poring over examples of the problem at hand. Minute samples of the troubling ‘blobs’ have now gone back to Lisbon for analysis and I have high hopes that we’ll soon know what it is we’re dealing with – and that this will give Léonie and her team the additional scientific insights they need in order to undertake genuinely appropriate conservation work on the windows. The day itself provided a wonderful opportunity to learn from each other in a spirit of partnership – although I rather suspect that I had the most to learn, by far – and I doubt I could convey its excitement adequately in the words of a blog post. In lieu of the better prose required I’ll end by sharing some of the images I captured from the day …
Phase 1: the journey up using the construction workers’ cage lift gave us some extraordinary views of the Bell Harry tower, some heavy-duty masonry, amusing gargoyles and down towards the Cathedral Gate and the city beyond.
Phase 2: the working platform sits atop a huge scaffolding assembly which straddles the nave a long way below; some sense of the height is possible using the left hand image, taken through a hole in the safety netting at the end of the platform and towards the quire and the altar. Even with the nave far below us, the space up there was still enormous. However, the key thing was being able to see some of the affected windows which are still in their original masonry settings.
Phase 3: poring over one of the windows now in the Glass Studio in order to get a better view of the ‘blobs’, which are all-too-evident in the left hand images (these show the same area of the window but viewed from either side – i.e. external and internal surfaces). Tiny amounts of surface material were then carefully removed for detailed scientific analysis.
Phase 4 & etc.: the results, conclusions and conservation decisions are yet to emerge; as in all areas of research, perhaps especially in the area of Heritage Science, patience is a virtue: watch this space …


Further reading
Although I spent a large fraction of my career as a scientist studying glass – there are innumerable entries on the subject within posts on my blog, e.g. here – I have come relatively late to stained glass and its conservation. However, for what it’s worth, these are the books that now sit on my shelves:

Paintings in Light by Martyn Barr, ISBN 978-0-9563429-4-2
Stained Glass of Canterbury Cathedral by M.A. Michael, ISBN 1-85759-365-0
Stained Glass in Canterbury Cathedral by S. Brown, ISBN 0-906211-31-X
Notes on the Painted Glass of Canterbury Cathedral by F.W. Farrar, a digitised version of the1897 original from bibliolife.com (I bought it online from a retailer specialising in out-of-print titles, here.)
Conservation of Glass by R. Newton and S. Davison, ISBN 0-7506-2448-5
The Conservation of Glass and Ceramics ed. by N.H. Tennent, ISBN 1-873936-18-4

Naturally, there is much also available online – both as text and as videos; you might like to take a look at the material uploaded from Canterbury Cathedral for example (e.g. here)

On the history of glass more generally, I find I have the following:
A Short history of Glass by C. Zerwick, ISBN 0-87290-121-1
Glass: a short history by D. Whitehouse, ISBN 978-0-7141-5086-4
5000 Years of Glass ed. H. Tait, ISBN 978-0-7141-5095-6
The Glass Bathyscaphe by A. Macfarlane and G. Martin, ISBN 1-86197-394-2



Monday, 8 May 2017

Colour my Glass


This is the first of a two-part post on glass, and in particular on the way in which light interacts with it. In this first instalment I’ll attempt to cover some glass basics: what glass is, its transparency, the way light behaves as it passes through and how one can introduce colours. Hopefully, this prepares the way for a closer look at stained glass in the second chapter and at a specific, Victorian, example of the sort of issues faced by conservators of Canterbury Cathedral’s stained glass windows.

Rather than spend a lot of time reiterating what I, and others, have written or spoken on in the past regarding what glass is, I’ll offer a brief description and then a couple of links to previous posts and videos. You can choose how wide-ranging you want to go, or how deep you’d like to dig – and by the same token, how long you want to spend on the topic. Perhaps the easiest place to start is via the assumption that most of us are familiar with what a crystal looks like. Even if you don’t have large diamonds or sapphires kicking around the place, you’ll have perhaps seen a crystal of quartz, or even grown salt or other crystals whilst at school. The one thing they have in common is the regularity of their respective shapes: all salt crystals are cubic, natural (i.e. uncut or polished) diamonds are, well, diamond-shaped and so on. The shape they display to us arises directly from the equally regular arrangement of their constituent atoms. Thus, the atoms in a quartz crystal – atoms of silicon and twice as many of oxygen – are also arranged regularly as though on an ever-repeating lattice. In this case however the atoms are arranged in a pyramid-like fashion (shown in the four-part figure below), which gives quartz crystals their characteristic shape. This provides for us a bridge into understanding glass, since the prototypical glass, silica, on which all our windows, bottles etc. are based, has an identical chemical composition to quartz: two oxygen atoms for each silicon atom. Just as in quartz, the atoms are in a pyramidal arrangement with their nearest neighbours – but the key difference is that silica typically solidifies too fast for the atoms to arrange themselves perfectly in 3D: the angles (and distances) vary just a little from one group of atoms to another. This addition of a small degree of disorder is enough to rob the material of any semblance of the regular facets observed with a crystal.
From left to right: a crystal of quartz, showing the regular facets associated with all quartz crystals which arise from the regular arrangement of atoms shown in the second figure (after Prof. A.C Wright). If the key angles vary by a small amount – less than 10 degrees – from one group of atoms to the next then one has the sort of disordered atomic arrangement depicted in the computer-generated model shown in the penultimate figure (after Prof. A. Cormack); it is this disordered structure that is associated with glass, as in the virtual MineCraft® building I wrote about here and which is depicted on the right.

Should you wish to read beyond this basic description I have written about glass, in its several guises, in several former posts, but this one is perhaps the most relevant; move on to this post if you would like learn something of the ‘human factor’ within scientific research into such materials. On the other hand, if you’d prefer to sit back and watch a video presentation on the subject, then look no further than the recording of a public lecture I delivered a few years ago in one of my local museums. The video is approximately 58 minutes long, although the introductory material is confined to the first eight minutes or so.

Having established the basics, and keeping in sight the target of understanding the way in which light is altered as it passes through glass – and coloured glass in particular – one ought first to tackle the matter of glass ‘transparency’. We tend to think of the windows in domestic and commercial buildings, windscreens, display screens etc. when we think about glass in the everyday. We can see through glass: it’s ‘transparent’ (see here for an excellent insight into why this might be). Indeed, the secret of the success of world-wide fibre optic communications resides in the exceptional transparency of the silica glass at its core, first demonstrated in the early 1970s by Donald Keck and co-workers. However, ‘ordinary’ glass isn’t perfectly transparent and might not be very transparent at all under certain circumstances. It all boils down to what sort of glass it is (its chemical composition, whether it includes bubbles, impurities & etc.) and what sort of ‘light’ we’re talking about. I have tried to illustrate this in the images below. The two images on the left show three types of glass: a common (soda-lime) glass typically used in windows, bottles etc. which sits inside a tube of Pyrex glass (a borosilicate) and which, in its turn, sits within the outer tube of pure silica. Viewed side on (left) the composite glass rod seems reasonably transparent, but when viewed end-on (middle image) so that we’re trying to look through a far greater thickness of glass it is obvious that the transparency varies a lot between glasses. Turning now to the diagram on the right, this illustrates the degree to which transparency, or the ability of the glass to transmit light, varies depending on what sort of light is involved. This simplistic diagram provides a representation of the situation with a car windscreen for example: of course we need a high level of light transmission for the visible part of the spectrum – the rainbow colours – but we don’t want a lot of infra-red or ultra-violet getting through as it’s preferable neither to overheat nor to get sunburnt; however, it is important that microwaves are able to pass through as our passengers may wish to use their mobile phones. The situation is very similar for window glass, and a great deal of research and development has gone into the formulation of glasses tailored to achieve these ends.
Please see the text above for an explanation of these figures.
Having now introduced some of the caveats and subtleties behind apparently simple comments such as “glass is transparent” we ought also to mention the important ways in which even transparent glass affects light as it passes through. Key phenomena are refraction and dispersion, which allow us to fabricate lenses and use prisms as well as to explain why a swimming pool looks to be less deep than it really is and where a rainbow comes from. Refraction is the phenomenon by which light is ‘bent’ as it passes from one transparent medium to another, and dispersion tells us that the magnitude of such processes depends on the wavelength – the colour – of the light. I’ll not weigh this post down with a lot of detail since it would be a bit of a diversion from the principal thread. However, if you’d like to know more then please take a look at two of my earlier posts: one on the origin of rainbows (here) and another which illustrates theories of colour through the use of a prism (here).

The final stage of this first post in the pair brings us to the subject of coloured glass. The reason that window glass is reasonably transparent is explained very well at the atomic level in the video I recommended earlier (here): in essence, there are few mechanisms within the glass able to reduce the amount of light passing through. We can change and control that situation, and do so by design. What is needed is the introduction of small concentrations of one or more metals, each of which will offer at least one route by which light of a particular colour will be absorbed. Thus, adding a metal which absorbs light at the red end of the visible spectrum (i.e. from the ‘rainbow colours’) ensures that the light transmitted through the glass has no red within it. We have, in effect, coloured the glass. For example, to give a blue-coloured glass one could use cobalt, copper or ferrous iron; nickel, chromium or ferric iron would yield a yellow-looking glass. Moreover, one can play with the addition of more than one type of metal. For example, a glass containing both ferric and ferrous forms of iron would appear green since that mid-section of the visible light spectrum would be the only part not absorbed by one or the other forms of iron. In passing, I had the privilege of taking part in a project run by the Turner Contemporary Gallery a few years ago in which the topic of colour was explored by a local group of young people. This included a visit to the Glass Studio at Canterbury Cathedral to examine the artistic use of such coloured glasses; the video record of the project is here and my short voice-over on the scientific background to the colours of glass starts at about two minutes in.
One can map the development of the chemistry of metals by looking at the coloured glass used by artists of the time. Within a very few years of their discovery, often less than a decade, a new metal would find itself being used within the glass industry. Some metals imbued not only a particular colour, but more exotic effects. Neodymium, for instance, will colour a glass blue in daylight – but this becomes more red in colour if the glass is illuminated with UV light (a ‘dark light’). Even more dramatic is the effect of UV on the green glass created by adding uranium – yes, uranium was used also – since it fluoresces and emits a very bright yellow-green light.

In the next post we’ll focus on one aspect of the artistic and architectural use of coloured/stained glass, and on the conservation issues associated with old stained glass windows. In the meantime, I’ll leave you with this image of one of the many delightful pieces to come out of Peter Layton’s studios; this piece is from his Mirage series.