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I stored water in a bucket (of aluminium probably), and some random fractal-like patterns are formed on the water:

enter image description here

See here for some more pictures.

Why did this happen?

I'm unable to reproduce it. How can I reproduce it again? Just leaving it alone openly doesn't work.

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    $\begingroup$ I have seen a similar film on the surface of water left in an opened tin can, also on a cup of tea, but not with such a pattern. This might be more a question of chemistry rather than physics. $\endgroup$ – sammy gerbil Aug 17 '17 at 23:00
  • $\begingroup$ According to Scum on the Tea the film could be calcium carbonate (chalk) which comes out of solution in still water. Why the patterns form might also be due to chemistry. $\endgroup$ – sammy gerbil Aug 17 '17 at 23:21
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    $\begingroup$ @sammygerbil Posted chemistry.stackexchange.com/q/81409 $\endgroup$ – Excel Hand Aug 18 '17 at 3:26
  • $\begingroup$ Just for curiosity: If it's calcium carbonate, there's also a plethora of biological sources, as discussed in this paper: ncbi.nlm.nih.gov/pmc/articles/PMC4718973 $\endgroup$ – stafusa Aug 22 '17 at 1:39
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It looks a lot like the result of diffusion-limited aggregation or more specifically diffusion limited cluster aggregation:

enter image description here

Image source.

If that's indeed the process responsible for the patterns, the question is then which particles are these. Likely candidates include dust and residues from previous use of the pot (milk, rice, etc.).

Edit: sammy gerbil's comment (and Ivan Neretin on the cross-posted Chemistry.SE question) suggest a chemical source for the particles: carbonates. The picture below (source) shows calcite particles aggregating into a lattice on the water surface of a stalactite drop.

Calcite precipitattion is well summarized in this Wikipedia entry, which describes (see also this thesis) how calcite growth is dominated by surface nucleation and coalescence and how (de)gassing of CO$_2$ from the water is a common process well known to lead to calcium carbonate precipitation.

enter image description here

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  • $\begingroup$ How van I reproduce the effect ? (Though storage of milk and rice of improbable and didn't happened}) $\endgroup$ – Excel Hand Aug 18 '17 at 8:02
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    $\begingroup$ If you leave the pot open for the same time it takes for the furniture in your place to acquire a visible layer of dust (about a week in mine) without cleaning, I'd expect it to happen again. (If you do the experiment, do report the results here!) $\endgroup$ – stafusa Aug 18 '17 at 9:17
  • $\begingroup$ No way that can happen. There are several instances where I kept a pot open, for several weeks, and this is there first time Im seeing this. $\endgroup$ – Excel Hand Aug 19 '17 at 12:39
  • $\begingroup$ There are too many variables (time of the year, open/closed window, etc.) that could influence dust settling and, of course, maybe the pattern is something else, not DLA. I wouldn't bet on bacteria, since they tend to form films (as far as I know), but maybe fungi could create those filaments (a quick search on that possibility didn't reveal anything, though). $\endgroup$ – stafusa Aug 19 '17 at 22:50
  • $\begingroup$ @ExcelHand, maybe calcite precipitation (see my reviewed answer) is our best lead - and then it's really a question for the Chemistry.SE to find out how to reproduce the conditions that led to this happening in your bucket. $\endgroup$ – stafusa Aug 22 '17 at 1:37

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