Skip Posted June 1, 2021 Report Share Posted June 1, 2021 I am new to pottery and even newer to throwing mugs. A person I gave a mug to today asked if there was any issue with pouring boiling water into the mug. I am throwing Standard clay 553 Buff Stoneware that I am bisque firing to Cone 06 and slow glaze firing to Cone 6 after painting on four layers of Amaco Potters Choice glaze. The mug in question has Ancient Jasper over Indigo Float. Any thoughts or advice on this are greatly appreciated. Link to comment Share on other sites More sharing options...
Hulk Posted June 2, 2021 Report Share Posted June 2, 2021 Hi Skip! Making a single cup o' tea == the test described, hence, subject your 7th favourite (perhaps not your very fav, any road) mug to it, as it's reasonable that mug users will. We don't want hot water flowing out of a split mug, for it's at least a disappointment and mess, and could be dangerous and damaging. As for your glaze, my guess is that you'd have seen glaze fit (crazing perhaps more likely than shivering) issues manifesting by now, if any. The thermal shock test might accelerate any fit issues, another reason to do the test, eh? I'm going with a clear or white liner glaze on my ware - no colours on the food/drink part, even though my colours seem rather durable, stable, and all - just not going there. Link to comment Share on other sites More sharing options...
Bill Kielb Posted June 2, 2021 Report Share Posted June 2, 2021 Well made with matching glazes and fully vitrified there should be no issue. That being said not many folks end up pouring boiling water in their mugs. Coffee is brewed at around 200 + degrees and cools rather rapidly to a lesser temperature just because of the vaporization. Most folks drink it around 140 with 160 being very hot to most and some outliers who claim they like it at 180 degrees. A bit bewildering to me as we consider 160 degree hot water from a hot water heater potentially scalding. Same with tea actually, it does cool fairly quickly pouring it in .......... fortunately. Anyway, well made mugs fired to a decent clays cone with good fitting glaze are pretty tough and should easily survive boiling water. Link to comment Share on other sites More sharing options...
Skip Posted June 2, 2021 Author Report Share Posted June 2, 2021 Thank you both so much for your quick, insightful replies. Hulk, I have a white glaze I will use in the future in my mugs. Bill, I will suggest using slightly cooler water for the reasons you mention. Thank you both!! Link to comment Share on other sites More sharing options...
Mark C. Posted June 2, 2021 Report Share Posted June 2, 2021 I would test my mugs by pouring boiling water in them as that is what many do to mugs. Then you klnow they can take it. I would do it many times as I know a few cycles can be a big difference . Link to comment Share on other sites More sharing options...
Min Posted June 2, 2021 Report Share Posted June 2, 2021 +1 for what Mark said. I go one step further than that and freeze some then pour boiling water into them and repeat this a few times. If they can survive this then you don't have to worry about cracking/dunting. @Skip, I would recommend doing this whenever you change glaze combinations. If you have a big difference in the thermal expansion rates of the glazes it can cause dunting of the mugs. Thicker glaze on the inside of a thin pot can exacerbate the problem. What people do with the mug(s) after it leaves your hands you have no control over. It's a reasonable expectation for mugs, cups, teapots etc to be able to withstand boiling water being poured into them. (I pour boiling water into a mug at least 3 times a day to make a mug of decaf tea) Link to comment Share on other sites More sharing options...
Skip Posted June 2, 2021 Author Report Share Posted June 2, 2021 Thanks Mark and Min. I’m going to do the freezer mug with boiling water test tomorrow. I did a room temp test tonight, and it worked perfectly. Link to comment Share on other sites More sharing options...
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