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flowerdry

Mug Broke With First Use.

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This was really embarrassing, and the first time this has happened to me.  I took some mugs to a friend and let her pick one out as a gift.  The next morning she poured boiling water into it for tea and the water came pouring out the bottom onto the floor!  I brought the box of mugs back and she settled for her 2nd choice.  I'm so grateful this was not a sale.

 

The mug was made with standard 112, using studio glazes, fired at the community studio which usually runs a high cone 6.  My mugs have a glaze catcher channel around the bottom rim and I use runny glazes.  The crack occured right at the glaze channel and ran halfway around the mug.  Liquid in the mug literally pours out.

 

Some folks at the studio looked at the mug and one thought was that the problem could be that the walls at the channel were very thin and a lot of glaze ran in there creating some tension.  The thermal shock was too much for it.  One person suggested that people should never pour boiling water into a room temperature hand thrown mug, but I feel like this is expecting too much from tea drinkers.  If they can't pour boiling water into the mug, then it's not a useful piece for them.  I have always poured boiling water into my and others' mugs without any problems.

 

Has anyone had this or similar problems?  I would appreciate any thoughts.

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Yes. I once got a phone call from one of my galleries ... a customer reported that my mug cracked when it met boiling water. I was mortified! I sent out a free replacement, and the gallery sent back the broken mug. The crack occurred along a latitude near the bottom of the mug where I had trimmed it too thin. Until then, my priority was to make mugs as light as possible, because I think that makes a mug more comfortable to use. But I changed my mind. Now my priority is "evenly thick throughout." My mugs are a little heavier now.

 

I agree with you that a mug should be able to withstand boiling water, so I am not willing to use that excuse. I can't really comment about tension caused by the extra glaze in your glaze catcher. My opinion is that the thinner wall was the sole cause.

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I pour boiling water in my mugs every week-they should take this well.

You have a thin spot in wall or foot or the wrong clay body or a tight glaze or something else.

You may want to try this on some other mugs you have.

I once did the same thing with hot water in a mug made with bad scrape clay from a friend the bottom blew out-that clay could not take the shock.

Mark

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Yes, from now on all my mugs are going to get the boiling water test.  I tested all the ones I have and found one more that didn't pass.  Not as dramatic as the other failure but I heard the cracking as the water went in and although I couldn't find the crack, there was a very slow leak if I left the water in the cup.

 

My mugs are also going to get a bit heavier.  Keeps the tea or coffee hotter longer anyway, right?

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