Why Does Water Soak Through Mugs?

[Identity]

When I pour a liquid into a mug, after a while of sitting, there will usually be a ring of liquid around where the mug has been in contact with the table. Assuming I haven't spilt any liquid, how does this occur? I'm sure this is a quite common phenomenon... are mugs simply not as 'solid' as they appear, or is something else at work?

 

[nasu]

It never happens with my mugs, unless they are already wet. I am thinking about coffee or tea mugs, that are warm.
If you have in mind a glass of beer then it makes sense.
If you pour cold beer in the container, the water vapors could condensate on the mug and then slowly drip down towards the base of the "mug".

 

[Molydood]

I have observed this on a number of occasions but don't know the explanation. My assumption was that some sort of absorbtion occurs initially and at some saturation point the mug stops taking on water and remains waterproof. I do find it weird that the water can absorb so far but not actually all the way through to the other side. I would like to hear the actual reason for it if anybody knows about the properties of ceramic in terms of water permeability.

 

[JaredJames]

A glazed mug (as most are) is waterproof. No water is absorbed into the mug itself. That is one of the purposes of glazing.

 

[pallidin]

It also is not uncommon that when we drink from a mug, not all goes into our mouth.
Some is left on the rim of the cup, some dribbles on the side.
From my own observation, I have never seen a carefully poured cup of coffee leave a ring on a table that has not been sipped from.
As noted from someone else, a cold beverage can certainly condense moisture in the air on the outside and eventually drip down.

 

[Rlam90]

Condensation?

 

[JaredJames]

Condensation?

From?

Consider what causes condensation and why you won't get it on a mug of coffee.

 

[cragar]

ok but you could get condensation from a cold glass of ice water.

 

[JaredJames]

ok but you could get condensation from a cold glass of ice water.

I've never said you couldn't.

I specifically asked about coffee, because the issue happens with both hot and cold beverages. Condensation may explain it for cold, but then what about hot?

 

[Topher925]

I've never seen this happen before. Can you take pictures? Does this happen when the liquid is at room temp?

 

[JaredJames]

I've never seen this happen before. Can you take pictures? Does this happen when the liquid is at room temp?

It's usually when some liquid spills down the side of the mug, collects around the 'ring' at the bottom, so when you pick it up there's a ring left on the surface.

Google: coffee ring (http://www.google.co.uk/search?hl=e...&q=coffee+ring&aq=f&aqi=g10&aql=&oq=&gs_rfai=)

EDIT: Note the fact that in those images you can clearly see the point at which the spill (or point of run down from mug) occurred.

 

[Molydood]

I should be clear that when I see it happen, it's not spillage from pouring, and I do not even see the rim of liquid underneath the cup - it is a liquid level drop inside the mug only. I figured that both observations could have same root cause (i.e. something to do with permeability)
I pour in the boiling water, and then over the span of about 5 or 10 seconds, the level appears to drop. I don't know if it's an illusion or if something more interesting is happening. I don't see it every time

Incidentally, there is nothing stopping steam condensing on inside of mug before the mug reaches a high temperature, but that is of course irrelevant :-)

 

[sophiecentaur]

I get this 'change of level' effect when pouring water over ground coffee in a cafetier but I think that's because the water takes a while to soak into the grounds.
Try your experiment with several different types of mug - including glass.
Perhaps your experimental mug has a poor glaze on the outside of the base. Perhaps it has wear on the bottom rim and can actually absorb water into its core whilst it is being washed. When you put hot water in the mug, this water will evaporate and condense on the cooler table top - making it look like water has come from inside the mug, whereas it's actually come from the porous pot core.
The reduced level of the liquid inside may be an illusion.

 

[Molydood]

Perhaps your experimental mug has a poor glaze on the outside of the base. Perhaps it has wear on the bottom rim and can actually absorb water into its core whilst it is being washed. When you put hot water in the mug, this water will evaporate and condense on the cooler table top - making it look like water has come from inside the mug, whereas it's actually come from the porous pot core.

I like this thinking.

(with regards to the level change thing, I will have to pay more attention when it next happens as your coffee example has got me thinking that it's something simple like dehydrated coffee granules causing the effect… duh!)

 

[sophiecentaur]

Try baking your mug in an oven at low temperature for an hour or so, then let it cool in a dry place. Repeat the experiment and let me know the result. We may have cracked it - the problem but not necessarily the mug.

 

[Molydood]

I have run a couple of basic tests:

TEST 1
Cup completely emmersed in water
Cup WIPED dry
Cup filled with HOT water
RESULT: water ring after 10 seconds

TEST 2
Cup emmersed in water
Cup WIPED dry
Cup filled with COLD water
RESULT: no water ring after 5 minutes

I am going to try the cup dehydration exercise tonight, and repeat the above two tests - my wife already thinks I am weird so no problem doing that

Incidentally, my colleague sat next to me is into pottery and she mentioned that the glaze is wiped from the contact patch before baking to prevent it sticking to the kiln floor, and I checked my cup and right enough the contact patch / ring is porous and glaze free!

Tonights experiments will confirm things either way, but I think you are correct Sophie :-)

 

[sophiecentaur]

Wives tend to be like that. Mine has completely given up on me about this sort of thing.
Good luck.

 

[JaredJames]

it is a liquid level drop inside the mug only. I figured that both observations could have same root cause (i.e. something to do with permeability)
I pour in the boiling water, and then over the span of about 5 or 10 seconds, the level appears to drop. I don't know if it's an illusion or if something more interesting is happening. I don't see it every time

Sounds like an illusion.

I'll throw this in anyway: evaporation?

 

[sophiecentaur]

Evaporation at what rate?
If you could notice a change of level due to evaporation then the temperature of the coffee would have dropped to undrinkable.

 

[JaredJames]

TEST 1
Cup completely emmersed in water
Cup WIPED dry
Cup filled with HOT water
RESULT: water ring after 10 seconds

TEST 2
Cup emmersed in water
Cup WIPED dry
Cup filled with COLD water
RESULT: no water ring after 5 minutes

Now what does cold do to a material and what does heat do to a material?

 

[JaredJames]

Evaporation at what rate?
If you could notice a change of level due to evaporation then the temperature of the coffee would have dropped to undrinkable.

When I wrote it I hadn't read the 5 or 10 second thing, I thought it was over a long period (say 30 minutes) of cooling.

 

[sophiecentaur]

If you're going to get involved with cutting edge Science you really will have to pay attention, you know.

 

[JaredJames]

If you're going to get involved with cutting edge Science you really will have to pay attention, you know.

I'm an engineer, not a scientist.

 

[nasu]

I have run a couple of basic tests:

TEST 1
Cup completely emmersed in water
Cup WIPED dry
Cup filled with HOT water
RESULT: water ring after 10 seconds

TEST 2
Cup emmersed in water
Cup WIPED dry
Cup filled with COLD water
RESULT: no water ring after 5 minutes

I am going to try the cup dehydration exercise tonight, and repeat the above two tests - my wife already thinks I am weird so no problem doing that

Incidentally, my colleague sat next to me is into pottery and she mentioned that the glaze is wiped from the contact patch before baking to prevent it sticking to the kiln floor, and I checked my cup and right enough the contact patch / ring is porous and glaze free!

Tonights experiments will confirm things either way, but I think you are correct Sophie :-)

What is the mug made of? I am sorry if you already said this. I did not see it.

Anyway, does the mug have any porosity? I don't mean pores that go trough, just surface pores. It may be that some water is absorbed in the pores and stays there even when you wiped it. If the pores are small enough (but not too small), some air may be trapped in the pores, behind the water. Heating the mug expands the air in the pores and it pushes the water out.
If this is the case, and if you try it after the mug was sitting for a while (or backing it, as someone else suggested) without dipping it in water before, you should not get the ring.

 

[sophiecentaur]

@jarednjames
Clearly the last post was also from an engineer!

We've been there already nasu.

 

[nasu]

@sophiecentaur
Sorry, now I've found your post on the previous page.
So this scenario was eliminated based on Molydood's observation that the level of the liquid drops. The OP himself seems to have lost interest, he did not give any details.

@Molydood
Still, what is the mug made of? It is some ceramic (maybe home made?) as I would guess from some your posts?

 

[sophiecentaur]

I don't think this is revealing any magic or Science - just wet pottery.

 

[Molydood]

Just to be clear, I think we have two unrelated effects that have been observed by different people
The 'level drop' observation is one effect and I suspect (in my case) it was observed when making coffee from dehydrated granules, which is likely to be the simple explanation
The 'liquid ring' observation is another effect and I suspect simply water trapped in base as already suggested above

I tried testing it out last night, but my wife would not let me put the cups in the oven (tsk) so all I could do was take mugs from the cupboard and hope that they had minimal water content in the base. Unfortunately, I could not generate liquid rings under the cups at all, no matter what I did
This morning, I tried using my cup in work, which was creating the effect quite reliably yesterday, thinking that the cup could have 'dried' overnight…. but now I can't generate liquid rings at all.

So it remains a bit of a mystery to me :-)

 

[Molydood]

@nasu, not sure on material, its just an off-the-shelf mug

an interesting side note however, is that the mug was actually a gift from the from the aforementioned "don't put my good mugs in the oven" wife - it has a periodic table printed on the side and it came from the Science Museum in London - so perhaps I should pay the museum a visit and ask them why their mugs produce inconsistent experimental results ;-)

 

[tuilli]

My guess is that the air trapped under the mug and close around it is warmed up, thus can absorb more moisture. Once the humid air comes in contact with the colder table, condensation ensues. You can actually see it happening through a transparent (eg. glass) surface.

 

[sophiecentaur]

@molydood
Your mug would only exhibit this behaviour when the pot core is a bit wet. A possible reason that it got water inside, initially, could be that it was hot, from being washed in hot water, then cooled down (right way up) in a puddle of water. This would have drawn water into the porous core. If you have dried it out it won't have any water left in it and you may have to 'prime' it by a repeat of the above process.
In view of the logo on the side of the mug, perhaps this phenomenon only occurs periodically !?

@tuilli
I don't think there would be enough volume in the space under the mug to hold enough vapour for it to show as significant condensation.

 

[DaveC426913]

I think you guys are hearing hoofbeats and thinking zebras.

I don't think the 'moisture on the outside of the cup' cause - either a stray drip or condensation - has satisfactorily been ruled out.

 

[sophiecentaur]

You could be right. I wasn't there to observe the details. And I think they're Gnus. Good Gnus.

 

[Molydood]

Sophie, I did try and resaturate the base but not exactly like you suggest - looks like I have something to do on Monday now. Liked the joke.
Truilli, i don't see why the water would form in a ring - quite the opposite as that is the hottest part of the supporting surface.
Dave, yeah, maybe you are right - I did try to be careful but in absence of a clear explanation I might have to accept it's just a 'duh' moment.

 

[tuilli]

I'd like to think that there is a continually changing micro weather system thingy going on within the tiny bubble of air under the mug :b
the mug or the table must be slightly damp from washing the cup or humidity or a spill, etc. the coffee heats the mug so its significantly hotter than the table underneath. The bottom rim will hinder the transfer of heat to the table and the heat difference between the table and the mug will still be big enough for condensation to occur. The trapped air bubble heats up, and absorbs moisture from the mug/table, the moist hot air condenses on contact with the colder surface underneath.
Condensation also occurs on a plate under a hot piece of toast..

Regarding the accumulation of water towards the edge, how about this: initially condensation occurs over the entire surface underneath the mug, avoiding the hotter outer rim but after some time the centre of the surface of the table underneath the mug gains the most amount of heat, causing the water on top of it to re-evaporate and then to condense along the now colder outer rim.