I have to give credit to my husband for this thought. ‘On no’, I hear you cry, ‘not him again’. This thought is about teapots.
Lasts week we were having a coffee / tea break together at a nearby restaurant-coffee shop-nightclub. He ordered tea. I had coffee. I am a bit of a coffee addict. He usually orders coffee so I queried his unusual choice. He said he was thirsty and he hoped that tea was more likely to quench his thirst than coffee. Then, as he started to pour his tea, he turned to me and said with some annoyance ‘why can’t I find a teapot that pours properly!’
I told him that I hadn’t ever found this to be an issue. In fact, I’d had tea with my mum earlier that week and I hadn’t remembered a badly pouring spout then. I thought back and couldn’t remember ever feeling annoyed at teapots.
So I decided to research this issue. The World Wide Web straight away throws up information about a distinguished Stanford University emeritus professor of mathematics who is known for the geometric theory of diffraction and something called the Einstein-Brillouin-Keller method, who is obsessed with badly functioning teapots. The chap is called Joseph Keller, and he is a well-known expert on why teapots drip, he is widely recognised for his thoughts on the matter. He is world famous for his teapot discoveries.
The Internet tells me he first felt the pull towards teapots after attending a lecture about the issue in 1956. In the lecture an experiment by Israeli scientist, Markus Reiner, was described. Reiner had asked 100 physicists why teapots drip. They had all concluded that it was due to surface tension. So Reiner then carried out some experiments that proved that dripping couldn’t be caused by surface tension. This drove Keller to write a famous paper called: The Teapot Effect. In this he concluded that the phenomena is in fact the result of fluid and mechanical forces. Rather than surface tension, the effect, he came to believe, is caused by air pressure. In other words, at the pouring lip the pressure in the liquid is lower than the pressure in the surrounding air. So air pressure pushes the tea against the lip and against the outside of the spout. The result? Drips.
Keller now prides himself on being able to spot a drippy teapot by just looking at it. If the teapot spout goes up and then down at the pouring end, the tea will flow back into the pot when the pot is turned the right way up again and a drip will then be almost impossible. Metal teapots with sharp pointy spouts are also good.
But if you don’t have a metal teapot with a sharp spout or a teapot that has a spout that goes up then down then the advice is don’t over fill your teapot. Overfull teapots lead to drips. There is science behind this. Tea from a less full pot will flow with greater speed. The speedier the flow, the less likely it is that the tea will stick to the lip.
Recently, in 2009, French scientists added to Keller’s teapot theories when they discovered that we also should consider the effect of ‘wettability’.
Wettability is a measure of how much a liquid likes being in contact with a surface. For materials such as clean glass, water tends to spread out. For superhydrophobic materials, such as the lotus leaf, water resists spreading.
So thanks to people believing in the teeny tiny possibility that those scientists who for years had thought that surface tension was the answer to the issue were wrong, we may yet get the perfect non-drip teapot.
My husband will no doubt be glad to hear this.