Amar Cafe means to love coffee. Though this is in Spanish. In Bengali it apparently means “my cafe”. This could perhaps lead to a short meander onto a language inspired thinking trail about how a cafe that you love to frequent becomes “yours” in a certain sense. Though to return to the coffee, the cafe itself is a small space located on Chelsea Green. There are other branches of Amar cafe in telephone boxes around London and in Stratford upon Avon. A couple of parking spots just outside the cafe have been converted to an outside terrace complete with small olive trees at which you can enjoy your coffee in the fresh air of the Green. Although this is clearly a Covid-19 related temporary measure, it would be good if some of these outside places can remain on a more permanent basis. They do add to the character of the Green. Amar cafe specialises in Colombian coffees that they source themselves. All of the usual espresso based drinks are available as well as the option of a pour over. A small selection of pastries including empanadas are available for breakfast. There are about four tables outside and a couple of tables (along with a window bench) inside. As you enter the cafe, the bar is immediately in front of you. Outside, the cafe is painted a bright yellow colour which makes it stand out among the independent shops that are in this little quarter of Chelsea.
On the two occasions that we have visited, I have enjoyed a really well made pour over each time. Although I am not good at generating my own tasting notes, I would say that the coffee was sweet and syrupy, with a fruitiness and complexity that was very enjoyable. It was presented in a V60 jug together with a black, handle-less, porcelain cup.
Gazing into the filter coffee, there were patterns on the surface of the coffee that you could see reflected at different angles. But looking more deeply, it looked black, within a black porcelain cup. Where did the cup end and the coffee begin? How could you see black on black? Which was blacker?
A material appears black to us when it absorbs the majority of the visible light incident on it and doesn’t reflect or emit any visible light back. Until 2019, the world’s blackest material was “Ventablack”, but even this material only absorbed 99.96% of the light shining on it. Late in 2019, a new material was discovered that absorbs 99.995% of light shone onto it. And not just that, it absorbs 99.995% of light from the ultraviolet to the THz (between infrared and microwave). The material is truly black. But the inventors of this material were not trying to make a black material, they weren’t even really interested in optics. The invention came courtesy of a collaboration with an artist.
At the time, Diemet Strebe was the artist in residence at MIT. The scientists at MIT who would go on to discover this new black material, were interested in the electrical properties of carbon nano tubes (CNTs). CNTs are a layer of carbon atoms (arranged in the hexagonal structure familiar for layers of graphite) wrapped into a tube. Each tube may be just a few nanometers diameter but they can grow hundreds of micrometers long. Depending on how they are wound into a tube, CNTs can have a very low electrical resistance. But this electrical advantage is lost when you try to attach them to a metal like aluminium because the surface of aluminium always oxidises. Unlike aluminium, aluminium oxide is a brilliant electrical insulator. Which is great if you want to study effects in which the electrical current is blocked, but terrible if you want to utilise these fantastically conducting CNTs. This was the problem that the scientists at MIT wanted to solve. Their solution was to remove the oxide using salt water and then deposit the CNTs on top. (When phrased like this it sounds such a simple idea, “why did no one do this before”, but there are many experimental steps needed to be able to grow CNTs onto substrates such as aluminium and it has taken many years to get to this point). Once the CNTs were deposited, the authors found that not only did they have a good electrical conductor, the material was really black.
What happened next is where the art comes in. Professor Brian Wardle who led the study was quoted as saying “Our group does not usually focus on optical properties of materials, but this work was going on at the same time as our art-science collaborations with Diemet. So art influenced science in this case.”
Thinking about how black the material was, the team decided to measure its optical absorption, which is when they discovered that they had broken the record previously held by Ventablack. And it was then that the art came back in. Strebe took a $2m natural yellow diamond and covered it with this ultra-black material. The result is striking (link). The composition, called “The Redemption of Vanity” could cause us to pause and ponder what we value as a society. What makes a sparkling diamond so valuable? How do we start to see objects by the fact that we can’t see them at all? If we extend this contemplation to our surroundings of Chelsea Green, we may wonder at this small little triangle of grass with its couple of benches. What does it reveal or hide? Does it help us to know that this is the last remnant of Chelsea Heath*, a bit of common land in which occupants of the surrounding manor houses down on (what is now) Cheyne Walk had the right to graze their livestock. Throughout this green, cows wandered up from the Thames as recently as the seventeenth century. A part of London that has disappeared, obscured by modern buildings yet held in memory by the street names and, the names of housing blocks.
As for why this material absorbs so much light, it is still an open question. It is known that the arrangement of the CNTs (including their alignment) can make a material coated in them very black. Even Ventablack is made from CNTs. It is a question that will probably continue to be discussed over many coffees. But is it a question that we would be asking again at all if it weren’t for the interaction in this case of art and science? Another point of contemplation that we can enjoy while looking into our coffee and just wondering ‘why’?
Amar Cafe is on Chelsea Green, 15 Cale Street, London, SW3 3QS and at several other telephone box locations.
*London Encyclopaedia, 3rd edition, Weinreb, Hibbert, Keay and Keay