Why Does Water Soak Through Mugs?

[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.

 

[sophiecentaur]

Your explanation bothers me because of the amount of water involved. I'm sure it needs another source, in order to produce visible condensation from such a small volume of air / waterproof surfaces.

Also, the outer rim would be cooler - not hotter. The top of the 'arch' underneath would be the hottest because it is furthest from the outside and right next to the hottest bits of coffee down there.
I will try it myself - with best porcelain and with cheap pot mugs.
How sad am I?

 

[tuilli]

..initially condensation occurs over the entire surface

of the table

underneath the mug...

 

[sophiecentaur]

I see what you mean now but still - how much water are you expecting to exist in that small volume of air?
You could prove it was possible by a calculation, if you wanted to.
And, in any case, unless the bottom of the mug was wet, there would be no more water (liquid or vapour) under it than when it was cold (immediately before the hot mug was placed there).

 

[JaredJames]

You could prove it was possible by a calculation, if you wanted to.

If anyone does choose to indulge us, we'll be wanting it in imperial.

 

[sophiecentaur]

Would you be wanting the answer in drams, gills, fluid oz or teaspoonfuls?

 

[JaredJames]

Preferably in Board Feet.

 

[DaveC426913]

per fortnight.

 

[Phrak]

Thank you all for a very entertaining thread. And if I may be so bold, I nominate sophiecentaur for Kitchen Scientist Extraordinaire, Plenipotentiary to the Queen.

In an indirect approach, does the exposed terracotta of a desicated mug evolve gas when heated in the expected time span? There must be some easy way to explore this. The best I can think of is to invert one in a deep bowl of water and nuke it.--maybe sink a few test mugs in a crock pot, bottoms up. That might do it. Tiny little bubbles of air on the bottom rims could tell us something if they appear.

 

[Molydood]

Tuilli, nice try but I still don't buy the condensing bubble of air theory I'm afraid - and I think you know it :-) I would expect a solid circle of liquid as opposed to a ring IF there was sufficient water content / humidity in the bubble under the cup.

 

[Molydood]

Phrak, I now have TWO things to do on Monday :-)

 

[JaredJames]

per fortnight.

And if I may be so bold, I nominate sophiecentaur for Kitchen Scientist Extraordinaire, Plenipotentiary to the Queen.

Seconded!

 

[tuilli]

Tuilli, nice try but I still don't buy the condensing bubble of air theory I'm afraid - and I think you know it :-) I would expect a solid circle of liquid as opposed to a ring IF there was sufficient water content / humidity in the bubble under the cup.

Ha I love it, drinking tea has become so much more complicated :b Still clinging on to the hot air bubble theory. Just to clarify, the air bubble will have the highest temp towards the centre, thus the part of the table directly under the centre of the mug will heat up most over time. Therefore condensation is more likely to occur towards the colder edge.
True, the air could not possibly hold enough water to form any noticable condensation. So, provided there is some source of water either on the mug or the table, the air will continually absorb moisture from that source until saturated, but the vapour also continually condenses on the table. So the volume of air doesn't determine the amount of water that ends up on the table. Rather, the air just acts as a sort of bridge to get the water from the mug pores or whatever on to the table... Haha the whole thing is ridiculous but can't get it out of my head

 

[JaredJames]

Ha I love it, drinking tea has become so much more complicated :b Still clinging on to the hot air bubble theory. Just to clarify, the air bubble will have the highest temp towards the centre, thus the part of the table directly under the centre of the mug will heat up most over time. Therefore condensation is more likely to occur towards the colder edge.

The mug will conduct heat far better than the surrounding air. The ring section at the bottom of the mug which contacts the surface will be hot. The coldest area initially will be the air at the centre where you claim it will be hottest. It's actually the inverse of what you are claiming.

 

[Phrak]

Phrak, I now have TWO things to do on Monday :-)

Me thinks the wife will be out of the house as coffee mugs go unguarded.

 

[Molydood]

I have performed the experiment again, this time being ultra careful not to spill a single drop of water anywhere, and also ensure that the exterior of the cup is completely free from any moisture. I have also tried using Sophie's suggested technique of saturating the porous base of the cup with cold water after the cup is already hot. I could not try Phrak's suggestion as I cannot see through the microwave door… a shame because the 'SPCM - society for prevention of cruelty to mugs' is currently not around to offer 'advice' which is a good opportunity for mug testing

FIRST experiment - dessicated cup trial
-cup hasn't been used for a few days so probably 'dry'
-I filled the cup with boiling water, wiped all exterior surfaces with a paper towel and let stand for 2 minutes
-no liquid rings appeared

SECOND experiment - saturated cup trial
-I heated up the mug by standing boiling water in it for 2 minutes
-I then inverted it and held under running cold water so that the concave base was being filled constantly with cold water… I did this for about 1 minute and then dried cup with paper towel
-I then filled cup with hot water, wiped all exterior surfaces with a paper towel again and let stand for 2 minutes
-no liquid rings

THIRD experiment
-I first wiped all exterior surfaces of the cup with paper towel and then I carefully placed a single drip of water on the rim of the cup (not the base, but the bit where you would drink from at the top) and then placed the cup on a table
-a liquid ring has appeared

CONCLUSION
a single droplet of water finding its way down the side of a cup can generate a full 360 degree liquid ring at base of cup - I believe this proves that I am an idiot who did not perform the original experiment very well - but I cannot say this for sure because I am not actually capable of performing experiments as I have just proved. I think that is a bit of a paradox - similar to saying "don’t believe anything I say because everything I say is a lie". I understand that paradoxes are (vaguely) scientific so apologies for going off topic ;-)

 

[sophiecentaur]

What an excellent piece of experimental work. Well done. Now you must send the documentation to Physics Review and get them to publish. You are clearly on your way to academic stardom. And it's not even near the beginning of April yet.

 

[Phrak]

THIRD experiment
-I first wiped all exterior surfaces of the cup with paper towel and then I carefully placed a single drip of water on the rim of the cup (not the base, but the bit where you would drink from at the top) and then placed the cup on a table
-a liquid ring has appeared

Clever. I wouldn't have considered that experiment. Yet it still leaves me wondering how much water the porcelain can evolve in extreme use. Do you have a pressure cooker?

And why aren't there any kitchen gadgets like autoclaves, centrifuges, or bell jar? There could be opportunity in providing these useful food preparation devices.

 

[Molydood]

Great idea; the centrifuge could be used for making mashed potato or tomato puree.
Bell jar could be useful for storing open bottles of wine to prevent oxidation
and who needs a dishwasher when they have an autoclave?