Artist Seb Lester creates calligraphy using in…

Artist Seb Lester creates calligraphy using ink and water, but not in the way you might expect. After writing in water, the artist applies ink a drop at a time, allowing fluid forces to spread it. There are a few effects at play here. Molecular diffusion – the random motion of molecules – can help two fluids mix, but it’s an extremely slow process. The fast, dramatic spread of ink seen in the video is more likely a Marangoni effect. The water and ink have different surface tensions, creating a gradient in surface tension that depends on the relative concentration of the two fluids. Gradients in surface tension create flow, which is why the ink spreads most quickly when it’s applied in an area that’s pure water. For similar physics, check out maze-solving soaps and the title sequence for “Marco Polo”.  (Video and image credit: S. Lester, source; via Gizmodo)