Why does coffee in a glass leaves its signatory on the surface?

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    Coffee Glass Surface
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Discussion Overview

The discussion revolves around the phenomenon of liquid rings left on surfaces by coffee cups, exploring the mechanisms behind how these rings form. Participants examine various factors contributing to this occurrence, including the effects of temperature, condensation, and potential spillage.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants note that the liquid ring may result from coffee spilling or dribbling down the side of the cup during use.
  • Others suggest that the phenomenon can occur with any container and may differ based on whether the liquid is hot or cold, with cold liquids potentially causing condensation that contributes to the ring.
  • A participant raises the possibility that residual water left in an inverted mug could also lead to liquid rings on surfaces, prompting an experimental approach to determine if thorough drying of the mug would prevent this issue.
  • Another viewpoint considers whether the ring could be caused by moisture in the wooden surface being drawn out by the heat of the mug, leading to condensation around the cooler edges.
  • One participant likens the inquiry to a "Sherlock Holmes problem," indicating the complexity and multifaceted nature of the discussion.

Areas of Agreement / Disagreement

Participants express various hypotheses about the causes of liquid rings, with no consensus reached on a singular explanation. Multiple competing views remain regarding the mechanisms at play.

Contextual Notes

The discussion includes assumptions about the conditions under which the phenomenon occurs, such as the temperature of the liquid and the material properties of the surfaces involved. Some claims depend on specific definitions of terms like "condensation" and "spillage," which are not universally agreed upon.

Zohar
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TL;DR
How does hot fluid comes down to the surface of the glass it's in?
Some of us may use coffee coaster for our drinks. I was always wondering about that phenomenon and failed to find something on the net yet.
 
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Zohar said:
Summary:: How does hot fluid comes down to the surface of the glass it's in?

Some of us may use coffee coaster for our drinks. I was always wondering about that phenomenon and failed to find something on the net yet.
Can you please restate the question, I am struggling to understand what you are referring to
 
Haven't you seen a circle of fluid under a cup of coffee? How does it happen?
 
Zohar said:
Haven't you seen a circle of fluid under a cup of coffee? How does it happen?

ohh ok, that's what you are referring to ...

Because the coffee has been spilt/dribbled down the side of the cup ... simple as that
 
Zohar said:
How does it happen?

it will happen on any cup, drinking glass, bottle of any liquid
and it will happen in a different way if the liquid is cold and it produces condensation
that then runs down the side of the container to the base. This is in addition to any
liquid that rund down the outside surface of the cup etc from what is dribbled/spilt
during the drinking process
 
Zohar said:
a circle of fluid under a cup of coffee?
I wonder if you leave your mugs on the side of the sink after washing them up. A small amount of water can stay in the inverted bottom and that can turn up on the table top. Experiment to find if drying up the mug totally will solve the problem. I can't think of any other reason.

Except if there is water in the wood(?) surface which is brought to the surface by the hot mug and then condenses round the cooler periphery to form a ring. Or is the ring in fact due to water and not just a temporary effect of heat on the varnish?

This is a Sherlock Holmes problem.
 

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