I am looking for what to call the solid or dust particles that reside at the surface of a liquid after density separation by flotation.

I had the term supernatant in mind, but I looked it up and it seems the supernatant is the liquid resting on top of another liquid or on top of a solid phase (the pellet) after centrifugation or similar procedure. What do you call the solid phase that floats at the surface of the supernatant after centrifugation?


During density separation by flotation, there are particles heavier than the fluid, and those will sink to the ground. Those particles can be called the pellet. However, there are particles, that are lighter than the fluid, and those particles will float. Assume you have tiny bits of candle wax in water. Those bits are so small that -- instead of floating right away -- they remain in suspension in the water. After sufficient centrifugation, the wax will float, since it is lighter than the water. What do you call the wax floating on top of the water? (Wax, obviously, but that's not what we're looking for in this example.)

  • Do you call it debris or flotsam or just precipitate? I did some searching and only 1 or two sites out of hundreds talk about more than two layers (pellet and supernatant) One talked about “oil and debris” the rest talked in specific terms about the actual things they were separating (lipids for example) I added flotsam on a whim especially in the case where that part’s not really what you’re interested in obtaining.
    – Jim
    Jan 7, 2018 at 19:42
  • 1
    On a somewhat larger scale, this can be called the float, as in a frothing table where an oil selectively captures particles and concentrates them by floating them to the top. Not sure about test-tube sizes, though. Floaties has a more respectable history than you might suspect. It seems to have come directly from M.E. flotesse.
    – Phil Sweet
    Jan 8, 2018 at 0:47
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    It seems to be called the float in metallurgy. I'll go with that or precipitate, although I like flotsam a lot, too, but I'm not sure it fits the purpose. 😏
    – thymaro
    Jan 8, 2018 at 1:02
  • There are two different things you might be describing: 1) Dust motes and the like that are suspended on the surface of the water by surface tension. 2) Solid particles which are less dense than water, and thus will inevitably float. I'm not sure which you're trying to describe.
    – Hot Licks
    Jan 8, 2018 at 1:04
  • The second one.
    – thymaro
    Jan 8, 2018 at 1:10

3 Answers 3


I know I am more than two years too late, but I'll still give it a shot!

I believe that the word you may be looking for is "scum."

"Scum" is defined as:

A layer of dirt or froth on the surface of a liquid. [Lexico]

  • 1
    I would have absolutely loved to use scum throughout my paper!
    – thymaro
    Jul 28, 2020 at 8:42
  • @thymaro Haha. Maybe next time...
    – user392938
    Jul 28, 2020 at 8:59

This is known as the pellet. But it usually resides on the bottom not top of the liquid after centrifugation.

From Wikipedia:

Precipitation is the creation of a solid from a solution. When the reaction occurs in a liquid solution, the solid formed is called the 'precipitate'. The chemical that causes the solid to form is called the 'precipitant'. Without sufficient force of gravity (settling) to bring the solid particles together, the precipitate remains in suspension. After sedimentation, especially when using a centrifuge to press it into a compact mass, the precipitate may be referred to as a 'pellet'.

  • Thanks for the answer. Unfortunately, the pellet is not what I am looking for. I should have pointed out the term 'pellet' as well. Going to fix it now.
    – thymaro
    Jan 7, 2018 at 18:46
  • Dust particles may form a film rather than a pellet. Jan 7, 2018 at 22:31

slag ( as in steel making where impurities float to the top)

  • 2
    Hi vakul! Thanks for answering. To show that yours is the right answer, please edit to include an explanation, context, and supporting facts. You can offer evidence, such as the definition from a good online dictionary, or contrast your answer with other answers. Whatever will make this the “right” answer. This is what makes answers useful – to the asker, and to future visitors. See: Real questions have answers, not items or ideas or opinions.
    – bookmanu
    Oct 16, 2018 at 10:07

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