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Reducing thermal conductivity

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Howdy all.  Can anyone share knowledge about reducing thermal conductivity of clay wares, other than making thicker walls? 

The story is: I'm slip-casting coffee cups in porcelain, and want to keep them light. They are lined with glaze to just over the lip, and the exterior is bare clay; I prefer this texture and look, but I know that a glaze will block some of the heat, so I plan on trying that.  Though, I wanted to ask you folks if you had insight into the problem.  Thank you for any help. 

 

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If your cups are intended for coffee, in the time it takes to drink a cup of coffee (10-15 minutes) it really doesn't matter if the walls are thin or thick, glazed or unglazed. 

A narrow top vs a wide top will help a little, but again the difference doesn't matter much.

The best way to reduce thermal conduction is to make a vessel with two walls, and a space of air between the walls. That might go against your wish to make "light" cups. 

Joseph F likes this

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Just spitballing here, as I have not tried this. If you used very soapy water for your slip, and used an electric mixer to foam/create bubbles, this might create air pockets which would be additional insulation.

Or mixing in fine sawdust might play a similar role. Then dip the greenware in a thin slip to smooth out any surface irregularities.

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Mugs are mugs. They've been essentially the same for a long, long time. People who like really hot coffee tend to use smaller mugs, and refill them often. Clay is not really the best medium for making insulated mugs- that's best left to stainless steel travel mugs.

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Thanks for the considered replies. 

I should've specified my aim: I want to keep the drinker's hands from getting burned. My porc slip body is quite conductive, and a fill-up at a coffee shop would make the cup too hot. There are other solutions (such as a sleeve), but these will be for production, and I'd like to solve the problem by dealing with the native form itself. Also, these will not have handles -- or the hot wall wouldn't be an issue. 

I am intrigued by the suggestion of putting air into the mix -- I've used perlite before to get a pitted/lava texture on sculptural pieces, but that's not the look I'm going for with these. I don't think a slip-dip would smooth out even a fine sawdust texture enough for my application here.  Thanks for the suggestion.

Any other ideas?

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You could make your cups taller, so the hot liquid would only fill the bottom two-thirds of the cups. The rim should remain cool enough to hold. 

You could add a tall foot ring, which should also remain cooler than the body of the cup. These cups can be held with a thumb on the rim and the remaining fingers on the foot ring. 

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2 hours ago, GEP said:

You could make your cups taller, so the hot liquid would only fill the bottom two-thirds of the cups. The rim should remain cool enough to hold. 

You could add a tall foot ring, which should also remain cooler than the body of the cup. These cups can be held with a thumb on the rim and the remaining fingers on the foot ring. 

I drink hot tea out of a cup without a handle. I do sort of what Mea said. I make a taller foot and I make the cup about 2-3oz bigger than the amount of liquid I plan to hold in it. Thus I can place the foot in the palm of my hand and my other hand's index/middle finger and thumb around the rim of the cup. I enjoy the experience of having to think about drinking my tea, it's neat thinking about what your doing. We consume things so quickly most of the time we don't even remember the act... Of course I am a nut job so maybe this isn't for everyone. 

So if you plan on making cups that are meant for holding 8oz, which is the amount of tea I like to drink in a cup, then make your cup for about 10oz, and have a decent foot so that you can easily place your hand there and not be worried about being burnt.

My wife is exact opposite, she doesn't like drinking out of a cup without a handle. So to each their own. I test my cups and she test my mugs. Good system like all marriages should be! muahaha

Edited by Joseph F

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Handles work best for HOT fluids-its a fact-all the other solutions for me are lesser. 

Yes handles are More work and cost more etc but they work the best.

The silicone sleeve is a good compromise but its all a compromise without a handle for HOT stuff.

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Handle-less cups.... the Japanese have a name for them.... yunomi.  They have a foot ring and are sized so that you grip them between the thumb on the lip and the middle finger on the footring....... solving the "hot on the hand" issue.

I don't doubt that working this thru on a 'high tech' level that some solution to the conductivity issue is POSSIBLE.. ...... just that it is not practical .... particularly at a reasonable price point.

Smooth ceramic shell over insulating material and so on.   Mugs for $1000 each.

best,

..........................john

 

Joseph F, Magnet and D.M.Ernst like this

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Thanks again for all the thoughts here.  

I reckon these are yunomi-of-sorts, though their use is more on-the-go... so they're just cups.  I also make guinomi and chawan, for their proper applications... maybe I should stick with them...

But I'm trying out a few practical solutions with glaze and other methods, so we'll see how it goes.   

Yes, too bad it's not easier to crank out a hundred double-thin-walled cups with cellulose-fiber cores... 

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A drinking vessel for hot beverages will usually be cooler than the hot liquid poured into the vessel -- handle or no handle!
  
If the outside of the container is hotter than you can hold with your hand, the liquid inside is guaranteed to be too hot to drink without damaging the surfaces in your mouth and  throat.
 
It is just pure physics.
 
LT
 
Joseph F and JohnnyK like this

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I was always taught if your going to drink a hot drink, you should warm up the cup before hand with hot water. So that when you put in your hot tea or coffee the cup is already warm so it doesn't pull heat from the liquid into the walls of the cup. Therefore the coffee stays hotter longer. I don't drink hot coffee but I do like tea. 

I agree 100% with what LT said. If the cup is to hot to hold, I sure am not drinking it.

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Just saw this thread now.  Why not a double walled mug?  They're becoming popular on etsy.  Some are gorgeous with pierced work and carving on the outer wall. 

Like these:  il_340x270.863075300_lz52.jpg

They may not be 100% functional in the reduction of thermal conductivity, but they look good?

Edited by Tyler Miller

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