crystallography

Reflections at Store St Espresso, Bloomsbury

Store St Espresso, coffee, Bloomsbury, UCL, London

Store St Espresso, Bloomsbury

I finally got around to visiting Store St Espresso two weeks ago while visiting the nearby Institute of Making’s 3rd birthday science-outreach party. Although the café was crowded, we managed to find a place to perch while we enjoyed a soya hot chocolate, caffé latte and my V60. Beans are from Square Mile while the V60 and filter coffee options featured guest roasters. Despite the narrow frontage, there is actually plenty of seating inside and people were happy to share tables with other customers when it got particularly busy. The café is well lit with sunlight streaming in through the sky lights above (indeed, the extra electric lighting indoors seemed a bit unnecessary given the amount of sunlight coming through the windows on such a good day). On the walls of the cafe were pieces of artwork, including quite a large pencil/charcoal piece right at the back of the cafe.

I was meeting a friend for coffee before going to the science event and so thought it would be good to combine a cafe-physics review with a visit to the science. It is always interesting to hear other people’s observations of the same space that you are ‘reviewing’. In this case, I was taken by the floor which showed some very interesting crack structures but what fascinated my friend (who was enjoying her caffe-latte) was the way that the sound from the stereo was reflecting from the bare walls, floor and ceiling. While cracks and fracture processes can be very interesting, perhaps it is worth following her observations as it leads, in a round about way, back to the coffee that she was drinking.

latte art, hot chocolate art, soya art

A caffe latte and a soya hot chocolate at Store St Espresso

While studying for my physics degree, a lecturer in a course on crystallography told us an anecdote. The story concerned a physicist walking past an apple orchard. As he was walking past, he noticed that at certain points he could hear the church bells from a distant church. As he walked on, the sound of the bells faded, before suddenly, he could hear them again. The physicist went on to derive the laws of X-ray diffraction, a technique that is now used routinely in order to understand the arrangement of atoms in crystals (like salt, diamond or caffeine). X-rays are part of the electromagnetic spectrum (just like visible light) but they have a very short wavelength.  The orchard had been inspirational to the physicist because, just as a crystal is a regular array of atoms, so the apple orchard is a regular array of trees; as you travel past an orchard (on the train, in a car or on foot), there are certain angles at which you can see straight through the trees, they have been planted in a 2D lattice. The church bells could only be heard at certain angles because of the way that the sound was being reflected from the multiple layers of the trees. The effect occurs because the sound made by church bells has a similar wavelength to the spacing of the trees (eg. ‘Big Ben’ chimes close to the note E, which has a wavelength of approximately 1m). The distance between atomic layers in a crystal is similar to the wavelength of the X-rays (the wavelength of X-rays frequently used for crystallography = 1.54 Å, size of the repeating structure in a salt crystal: 5.4 Å, 1 Å = 1/100000 of the smallest particle in an espresso grind). The physicist realised that the orchard affected the church bells in exactly the same way that the atoms in a crystal, be it salt, diamond or caffeine, will affect the deflection of X-rays. Suddenly, it became possible to actually ‘see’ crystal structures by measuring the angles at which the X-rays were scattered from substances.

bubbles on a soap solution

Not quite a regular 2D lattice. By controlling the size of the bubbles and the number of layers, you can simulate the crystal structure of different metals. Seems I need more practice in making bubbles of a similar size.

We can perhaps imagine an apple orchard but what do crystals look like? Crystals can come in many forms, all they need to be is a repeating structure of atoms through the solid. Some crystals are cubic, such as salt, some are hexagonal, others form different shapes. Metals, such as that making up the shiny espresso machine in the cafe are often a certain form of cubic structure and to visualise it, we can return to my friend’s caffé latte (via some soap). Two people who were instrumental in understanding X-ray diffraction were the father and son physicists, William Henry and William Lawrence Bragg. While attempting to make a model of crystal structures, William Lawrence Bragg found that the bubbles that could be formed on top of a soap solution were a very good approximation of the sort of crystal structures observed in metals (his paper can be found here). As they form, the soap bubbles (provided they are of similar size) form a regular cubic structure on the surface of the soap solution held together by capillary attraction, a very good model for the sort of bonding that occurs in metals. By controlling the size of the bubbles, the number of layers and the pressures on the layers of the bubbles, all sorts of phenomena that we usually see in crystals (grain boundaries, dislocations etc) could be made to form in “crystals” formed from soap bubbles. Why not look for such crystal structures in the foam of your cafe latte, though be careful to see how the size of the bubbles affects the arrangement of the bubbles through the foam structure.

Sadly, I have never found a reference to the story of the physicist and the apple orchard and it may even have been apocryphal. The closest reference I can find is that W. Lawrence Bragg (after whom the laws of X-ray diffraction are named) had a “moment of inspiration” for how X-rays would ‘reflect’ from multi-layers of atoms while he was walking in an area called “The Backs” in Cambridge. If any reader of this blog does know a good reference to this story I would be very much obliged if they could tell me in the comments section (below). To this day, I have been unable to pass by an orchard (or even a palm oil estate in Malaysia) without thinking about crystal structure, X-ray diffraction and church bells!

It seems that taking time to appreciate how sound is reflected (or diffracted) from objects, either in Store St Espresso or in an apple orchard, could be a very fruitful thing to do. If you have an observation of science in a cafe that you would like to share, please let me know here.

Store St Espresso can be found at 40 Store St. WC1E 7DB

The physics of X-ray diffraction and some great bubble crystal structures can be found in the Feynman Lectures on Physics, Vol II, 30-9 onwards.

Crystal Perfection at Workshop, Holborn

Workshop coffee Holborn

Diamonds are forever, Workshop coffee Holborn

The brand identifier of Workshop coffee is a diamond, a representation of which hangs on the wall as soon as you enter the Holborn branch. I had arrived at Workshop in order to try their coffee after I’d had a great espresso made with beans roasted by Workshop at Knockbox in Lamb’s Conduit Street. The coffee brewed in their own café certainly did not disappoint. I enjoyed a very good La Soledad filter coffee and a cake (which was confidently nut free, this brings me to another plus point for Workshop, they know the ingredients of their cakes!). The interior of the cafe, just beside Holborn Viaduct, is quite spacious and, if you sit at the back, you get a great view of the workings of the espresso machine as different people come in to get their ‘take out’ coffee. It is very possible to spend quite some time here in order to relax and enjoy your coffee while taking in your surroundings. To a physicist who studies materials (like me), the diamond logo of Workshop represents a fantastic material. A material in which the structure of the crystal determines so much about its properties. Were the carbon atoms in diamond bonded slightly differently, they would form the soft, pencil lead material ‘graphite’, rather than the hard, transparent material of diamond.

unit cell, repeating structure

The floor at Workshop reminds me of my crystallography text books.

Whether it was intentional or not, the crystal theme of the logo was replicated in the floor tiling of the Holborn branch. Crystallography is a branch of science that probes the building blocks of solids. It reveals how the atoms that make up different solids are arranged to form the solid. The atoms could be arranged in a simple cubic arrangement (as with salt) or hexagonally (as is the case for graphite). To establish the crystal structure you need to find the smallest repeating unit in the whole. Many introductory solid state physics or crystallography text books use 2D examples of repeating structures to help the student to understand how to build up these “unit cells” into full blown crystals. Many of the examples of such lattices look stunningly similar to the floor at Workshop.  Fundamentally, the idea of the crystal is that it is a simple repeating structure, just like the floor of Workshop. Indeed, the word “crystal” as used by Pythagoras implied perfection, harmony and beauty, a sense that is really conveyed by the crystal structure of the diamond logo of Workshop.

Crystal cake, LaFeSi cake, grape atoms

When a colleague left our lab, we made her a  cake that was a representation of part of the crystal structure of the material that she had worked on. Chocolate grapes and profiteroles represent different atoms in the structure.

The ancient Greek term for “crystal” actually implied the type of hard ice that is wonderfully clear and transparent. And it is ice that connects the area surrounding Workshop with a famous chemist who won a Nobel prize for his work in crystallography in 1962.  Max Perutz (1914-2002) described crystallography as a technique that “explains why diamond is hard and wax is soft, why graphite writes on paper and silk is strong”. Once you have enjoyed your coffee at Workshop, if you head down the stairs on the viaduct and descend to Farringdon Road you quickly get to Smithfield Market. It was here that, during the Second World War, Perutz helped to develop the material Pykrete. A “secret weapon” of World War II, Pykrete was developed five floors below Smithfield Market in a room cunningly disguised with animal carcasses. The planners in the war effort had wanted to design a boat made of ice but the problem was that when it was shot at, ice shattered. Could scientists develop a type of ice that would not shatter if it got hit by enemy fire? Pykrete was the answer. Pykrete uses the fact that materials such as plastics can be strengthened by adding fibres to them. In the case of Pykrete the “fibres” were sawdust and the material to be strengthened was ice. Not only does it not shatter when shot at (instead, the bullet creates a crater in the ‘boat’), it takes a lot longer to melt than ordinary ice. The sawdust encased in the ice acts to insulate the ice and increase its longevity.

Perutz’s Nobel prize was for his work to determine the crystal structure of haemoglobin, it took ‘just’ 25 years to do so. The field of crystallography continues to enrich our understanding of the behaviour of solids, though now we’re expected to get results more quickly than the 25 year time frame Perutz enjoyed. If you know of a good café where lots of physics goes on, or of a good café near a site of special (or unexpected) scientific interest, (or even just a good café) please do share your story either in the comments section below or by contacting me on email, Twitter or Facebook.

Workshop Holborn is at 60 Holborn Viaduct, EC1A 2FD

Quotes and other useful facts taken from:

In our time, 29th November 2012: Crystallography“, (BBC Radio4)

Max Perutz “I wish I’d made you angry earlier” (2002),

Ichiro Sunagawa “Crystals, Growth Morphology and Perfection”, Cambridge University Press (2005)