These days we have a lot of new gadgets to help out in our daily lives. Two of these — the dishwasher and the microwave — have the potential to damage our ceramic tableware and other ceramic items. Follwing a few simple rules will help to avert disaster. Let’s start with dishwashers.
Dishwashers and Ceramics
Dishwashers are quite harsh when cleaning. They use extremely hot water and abrasive, possibly corrosive chemicals to get dried up grime off your dishes. This means that your ceramic items will get quite a battering in the dishwasher. Usually a manufacturer will specify whether ceramic tableware or dinnerware is dishwasher safe, but if in doubt, you should be safe if you take heed of the following.
Porcelain and stoneware is generally safe, except if there are decals or onglaze lustres, e.g. gold on the surface. Sometimes porcelain is glazed at a lower temperature. In this case, the glaze may not be so strong and subject to eventual degradation in the dishwasher. If the glaze scratches easily, this may be the case.
I generally wouldn’t recommend to clean earthenware utensils in the dishwasher as these are not fired as high as stoneware and thus more vulnerable.
First of all, no metals should be used in microwaves. This will cause ‘arcing’, i.e. a spark jumps from the microwave to the metal, possibly damaging the unit. This means that ceramics with metal lustres or onglazes such as gold, silver and copper, should not be microwaved.
Secondly, microwaves heat food by agitating water molecules, which then get hot. If a ceramic dish or cup is low fired, it may soak up some moisture into the clay body. If this moisture gets heated enough, it will turn to steam and expand, possibly causing an explosion. Not only would the ceramic item be lost, but the microwave might sustain considerable damage. Because of this, I would recommend to only microwave porcelain and stoneware, or earthenware that is vitrified enough not to soak up moisture. If in doubt, hold the piece on the palm of your hand. Carefully knock it with a knuckle (make sure you don’t knock it to the ground!). If there is a clean ring, the piece should be dry, whatever it is and probably safe to microwave. If it sounds dull, it probably has some moisture in the body — it would be better not to risk it. (If it sounds really dull, with a short ‘buzzing’ sound to it, there probably is a crack somewhere.)
- DO wash stoneware and porcelain in the dishwasher
- DO microwave stoneware and porcelain
- DO put a rubber nozzle on your sink tap, to prevent chipping when hand washing
- DO put a paper tissue between fine china when stacking items on top of each other
- DO be careful with fine rims and handles – they are most vulnerable
- DON’T wash ceramics with decals or lustres in the dishwasher
- DON’T put ceramics that have a dull ring in the microwave
- DON’T put lots of dishes in the sink when hand washing
|Linda Arbuckle kindly submitted the following comments:
“In response to the article about microwaving…. I’ve had some stoneware cups heat up enough in the microwave to make the handle uncomfortable to hold. I find wood/salt/soda pieces are often not vitrified and have this issue, but it’s also happened with reduction-fired wares. I have heated fake bacon strips on a porcelain plate and had it crack in 2 (too much localized heat for a dense body), while earthenware baking dishes have been no problem. I do microwave Stan Andersen’s majolica plates regularly with no problems. I don’t think it’s accurate to advocate no microwaving for earthenware as a group while recommending stoneware and porcelain carte blanche. It just isn’t so. Depends on the clay body, firing, and glaze.
I daily microwave my majolica-glaze earthenware cups to make tea (they do have terra sig on the foot), and they do not explode or heat up in any uncommon way. They haven’t even crazed.
I think there’s a lot of “iffy” advice out there about earthenware. The advice on DO microwave stoneware and porcelain and DON’T microwave earthenware is like everything else in ceramics: it all depends.
So many of the pottery “sources” knock earthenware w/o really having solid facts. When I was a student, many of the high-fire gurus indicated there was nothing worth doing in earthenware, and even then, leaded was the only way. As an aside, Pete Pinnell has some interesting info on clay body strength. I’ve appended that below.”