# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DcMXTNAvrQj
- **Gondola URL:** https://gondola.cc/posts/69422664-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/388c8e4c67.jpg
- **Posted:** 2026-08-18T19:28:46.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

The sun in this frame is a few millilitres of alcohol ink in a Petri dish. No animation, no simulation, just surface tension losing an argument with itself.

Alcohol inks are dye or fine pigment carried in isopropanol or ethanol. That carrier has a surface tension near 22 millinewtons per metre. Water sits at roughly 72, more than three times higher. Put one into the other and the interface cannot stay still, because the surrounding high tension liquid drags the low tension patch outward in every direction at once. This is the Marangoni effect, and at macro scale it is violent: spreading fronts cross a dish smaller than a coin in a fraction of a second.

What turns a spreading blob into a corona:

- Viscous fingering. When a thin, mobile fluid displaces a thicker one, the interface is unstable. Any bulge advances faster than its neighbours and runs away, splitting again and again into the branching filaments that read as sunbeams.
- Evaporation. Alcohol leaves first, so the film left behind grows richer in water and higher in surface tension. The gradient regenerates itself, and the flow pulses rather than settling.
- Pigment as tracer. Solid particles cannot follow the fluid perfectly. They pile up along stagnation lines and dry into the grain and speckle in the outer ring, a fossil record of the flow field long after the liquid has gone.
- Optics. At this magnification depth of field is a fraction of a millimetre, so light pushed up through the dish is doing work no key light could.

The chemistry is trivial. The physics is not, and no two runs will ever produce the same structure.

Beauty here is not decoration, it is an instability caught mid collapse.

#stemantics #fluiddynamics #marangonieffect #macrophotography #physics

## Stats

- **Views:** 5,836
- **Likes:** 136
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- **Comments:** 2

## Tags

marangonieffect, fluiddynamics, physics, macrophotography, stemantics

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