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

[Zohar]

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.

 

[davenn]

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

 

[Zohar]

Haven't you seen a circle of fluid under a cup of coffee? How does it happen?

 

[davenn]

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

 

[davenn]

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

 

[sophiecentaur]

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.