I mean, I put them through the dishwasher sometimes anyway, but I’m told I shouldn’t? 🤷🏻♀️
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It’s not the ceramic that you risk breaking, but rather the finish that is of concern. Putting delicate paints and finishes in the dishwasher is all but guaranteed to scratch and ruin their costing.
The heat isn’t the issue, the detergent is. Ceramic absorbs water very easily, including the detergent. But detergent isn’t fit for consumption, yet it would leech out into your drink.
It isn’t about the heat but about the moisture. Ceramic isn’t fully waterproof and the water will sit in the pores of the material. Over time this will make the mug crack.
I took 4 quarters of ceramics in college. I absolutely loved it. Our instructor made sure all glazes were dishwasher and microwave safe. And did not allow any glaze that was not to be fired with students projects.
I can’t imagine many others doing differently.
the whole ceramic piece has to be glazed all over, or the water issues others mentioned with be a problem
It is not the heat that is the problem it is the water. If it is not glazed it is porous and water getting into it that is the problem.
What is also stated is that hand-painted ceramics should not be put in the dishwasher, that is to protect the paint. That sounds quite reasonable.
I have not tried that myself, that is because I do not use that type of ceramic so I do not know if that really is a problem. It is stated online and by some manufacturers of dishwasher detergent. It looks like part of the problem is that it can absorb the dishwasher detergent and it can get into your food. Dishsing a cup by hand is not hard so I would just do that and avoid the dishwasher.
https://bigtimekitchen.com/pottery-in-dishwasher/
Usually it’s fine. They can go in the microwave too (maybe better not with a metallic glaze). If they had water trapped in the clay somewhere, the thing would have cracked in the kiln.
The glaze might not be as sturdy. You can see that in industrially made things too, the glaze cracks all of a sudden. It’s called “crazing” and happens when the glaze is under stress. Again, not so much of an issue in itself, it’s just the glaze, the cup won’t break completely along those lines. But it’s no longer perfectly sealed there. Water (and with bad luck bacteria) can get to the way more porous clay. And heating a crazed cup that has soaked up water suddenly (microwave, dishwasher on hot, or just pouring hot water in) could chip fragments of the glaze off or break the cup.
But usually it’s fine. That’s like the labels on wool or silk clothes “dry clean only”, there can be reasons for it, but that it’s wool/silk is *not* it. Sheep don’t shrink in the rain.
It depends on the ceramic, some are dishwasher safe and some are not. Fully vitrified clays (fired at a high temperature) don’t absorb water and are dishwasher safe. Some ceramics are fired at a lower temperature, are porous, and are not dishwasher safe.
Potter here…
This is a complicated subject. Well-made and tested homemade ceramics can go through the dishwasher just fine. However, a dishwasher is a very rough environment. Most potters, who recommend handwashing only, do so because the pot is less likely to get banged around. Stress cracks, formed by banging against another pot in the dishwasher, can cause the entire pot to crack when hot liquid is poured into it, not to mention chips and dings to the rim.
Other considerations: Dishwasher detergent is very basic. If the glaze is not tested for basic conditions (rare in foods) a dishwasher can cause the glaze to fade over time. Also, there are certain finishes, such as gold enamel, that will fade badly in the dishwasher. Finally, if the clay body is not fired to low absorption, a dishwasher can cause water absorption in the clay, which can cause mold and excessive heating in the microwave.
So, for dishwasher, microwave safe ceramics, the clay body and the glaze need to be tested together for fading under both acid and basic condition, no enamels applied, and the clay body should be fired high enough to ensure a low absorption. It is highly recommended that each clay body be tested by the potter prior to use. It’s not uncommon for manufacturers to label a clay cone 6-cone 10 when the clay is not really suitable for functional use when fired to cone 6.
I’m probably forgetting something, but these are the use cases that affect my work.
EDITED: Corrected a term. It’s “basic” not “caustic”. Thanks to ScienceIsSexy420 for pointing that out.
I thought it would be for the same reason you don’t wash china and crystal.
The detergent has micro-abrasives to help scrub and a glossy surface can be dulled by them.
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