I've been measuring the specific gravity of the color-coded plastic media. The sieve fractions that I separated earlier yielded some interesting preliminary results:
These represent single measurements - so there may be a lot of variation that's not accounted for. I used a volumetric flask and vacuum method to remove the air bubbles. The white fraction did appear to generate more bubbles than the other color fractions, so perhaps there is something inherent in the material to explain why they seem to have a slightly lower specific gravity. Does this influence how the material sorts itself during a stream run? Maybe, but there's lots of other fluid dynamics stuff to consider, too.
Here's one of
Steve's Time-Lapse videos showing how running water can generate gorgeous color patterns.
Steve Gough posted a comment, but it was eaten alive by Google:
This is super interesting to us at LRRD! We ran a lot of specific gravity tests as we developed the media; and found very close clustering, but more at about 1.60. I'm not too concerned about a 0.05 difference between colors, but if it got bigger I would be! Melamine has very low water absorption (for some plastics it can be 10% plus), but it's possible that's part of the problem; you might try soaking all the samples for a few days before testing. Thanks!
Neat! Thank you for sharing this.
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