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Comment by simulate-me | Hacker News Reader

Is capillary action not a satisfying enough answer for you?

Capillary action requires narrow channels. Single surface shouldn't work, at least intuitively. Some might argue that any tiny crystal formed creates narrow channels between the crevices, wicking out more of the liquid and speeding up outward crystal growth. But even that is something I came up with off the top of my head, and I wouldn't find it credible without a better source than my shower of thoughts.

This mechanism is mentioned in the Chemistry Stack Exchange question linked by the OP.

> Indeed, capillary effect is enough. New portions of solution get higher and higher up, and deposit crystals to build more capillaries, much like a horde of guys with ladders storming some medieval fortress.

I suspect that the capillary action is started by microscopic scratches in the plastic formed when the plastic cups are removed from the molds they were shaped over. This may explain all or some of the capillary effect.

Should be easy to verify by suspending some surfaces ~1cm away from the side of the container to see if there is any deposition occurring by vapor.

It happens in glass too, as shown in one of the pictures.

Glass can have microscopic scratches that act as capillaries. Somewhat related: I remember one of my undergrad chemistry practicals where we had a supersaturated solution in a test tube. Scratching the inside wall of the tube produced tiny glass shards that induced precipitation of the solution.

I don't know much about chemistry so the two word answer "capillary action" wasn't enough, but now that I see it I will do more research.

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