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I have a jar of honey that has a load of gold flakes suspended in it. It has been sat still for 24 hours and the flakes have risen to the surface. At least the bigger parts and the small ones stayed as they were. Any ideas as to the physics behind this and also if its possible to prevent the bigger ones from rising to the surface?

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Gold is denser than honey. It should sink. You can see here that it does.

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On the other hand, you can see here that it floats.

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The difficulty is that gold foil is very thin, $0.001$ inch or less. When added to honey, an air bubble often is attached. Air floats.

The same problem applies to Murano glass. This is art glass with gold flakes in it. The problem isn't that the flakes will float. But bubbles don't look good. The manufacturer has figured out how to avoid bubbles.

It look like one brand of honey has figured it out and the other hasn't.

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  • $\begingroup$ Could surface tension be at all relevant? Honey has a surface tension of 50–60 mN/m (at 298 K, naturally), whereas water has a surface tension of 72 mN/m. While the surface tension of water is higher (and certainly relative to its viscosity), it doesn’t seem to be so much higher that it could be ruled out. Could the gold flakes simply have been sprinkled on top rather than being mixed in (the latter of which I think would make surface tension irrelevant)? Alternately, even if they did float to the top because of air bubbles, surface tension could be the main barrier to sinking back in. $\endgroup$
    – Obie 2.0
    Jun 11 '17 at 17:58
  • $\begingroup$ @Obie2.0 The OP said that bigger flakes float to the surface, while smaller flakes do not. This implies gold by itself doesn't move as fast as air bubbles. This makes sense. Gold leaf has a lot of surface and not much weight. Honey is viscous. Given that, it could well be that once gold reaches the surface, surface tension helps keep it there. $\endgroup$
    – mmesser314
    Jun 11 '17 at 23:57

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