Dishwashers are magical machines. They have the power to change a sink full of dirty plates, glasses, and flatware into a tub full of sparkling ready-to-eat-off dishes. They have the ability to alter the passage of time, giving you more of it to spend on more interesting activities than washing dishes. But the magic doesn’t work on everything. There are some things (see above photo, credit Jalopnik) you should never, ever put in the dishwasher.
1. Anything That’s Not Kitchenware
Every so often, you may come across someone on the internet advising you to go ahead and use your residential kitchen dishwasher as an industrial degreaser. Should you get such an idea in your head, first read this cautionary tale from someone who attempted to clean the timing chain cover that came off a 30-year-old Jeep engine and wound up eating off of plates that were spotted with an oily residue for nine months (!) afterward. And his timing chain cover was not a bit cleaner. So don’t do this. Especially if you are married.
2. Anything Glued
You loved your old coffee mug. It was special, a part of your morning ritual. You’d used it for at least a decade. It had sentimental value. So when your Schnauzer knocked it off your coffee table, you glued it back together. (Your mug, that is; not your Schnauzer.) But from then on, your mug’s days in the dishwasher are over. Same with plates and anything else that’s glued together. The heat and detergents in your dishwasher will weaken or melt the adhesive, making it harder to glue together a second time.
For the same reason, hollow-handled knives are a no-no in the dishwasher, unless the manufacturer designates them as dishwasher-safe. They’re held together with glue too.
3. Anything Cast Iron, Wood, Brass, Bronze, Copper, Aluminum, Acrylic, or Most Types of Plastic
Dishwashers are great for cleaning everyday plates, flatware, glasses, and some kinds of cookware. But things made from any of the above don’t belong in the dishwasher. The “seasoning” on your cast iron pans will be washed away and your pan will be prone to rust spots and food stickage. Your copper pans and that special copper mug you use when you make Moscow Mules will become dull and discolored. The same is true of anything made of bronze, brass, pewter or aluminum. Wooden utensils will warp and crack and lose their finish, developing a dry, cracked surface. Wooden cutting boards that are glued together will actually fall apart. Some hard plastics are dishwasher safe, but even those should be washed only on the top rack.
4. Anything Holey
No, we’re not talking about religious artifacts. We’re talking about kitchen gadgets with holes, especially small holes: cheese graters, garlic presses, microplanes, cherry pitters, cookie presses, sieves, sifters, meat grinder plates, potato ricers, food mills, tea strainers, and the like. Dishwashers are not designed to clean food particles out of small holes and crevices. Food that gets stuck in those nooks and crannies may actually become something like a gummy paste when exposed to hot water and detergent. Clean these items by hand with a sponge and soapy water. A toothpick can be used to dislodge particularly stubborn food particles.
It’s important not to put pressure cooker lids—especially ones that were made in the 1950s and earlier—in the dishwasher. These lids used a weighted pressure relief valve that can become stuck or clogged when tiny food particulates come to rest in them and are then baked on in the drying cycle. For safety’s sake, these items should be hand washed in warm water, rinsed thoroughly, and hand-dried before they are put away. Modern pressure cookers and Instant Pots have a somewhat different safety valve design, but manufacturers still recommend that they be cleaned by hand and/or with a toothpick.
5. Anything Old
Your old Scooby Doo drinking glasses. (“Fred, Velma, Daphne, Shaggy, and Scooby—collect them all!”) Your grandmother’s handpainted stoneware she picked up on her honeymoon in Pago Pago in 1957. Those ugly antique Hummel figures your weird father-in-law gifted you with and that you have to display every time he comes to visit. That cool set of semi-opaque milk glass dishes you snagged at a garage sale. Your old Vanilla Ice albums. If it’s antique, vintage, handmade, delicate, and/or of great sentimental value, it’s far better to clean it in the sink with a dish towel lining the bottom. The detergent, heat, and vibration that come with dishwashing are just not good for old things.
6. Anything Labeled
Pro kitchen tip: spaghetti jars are great for storing leftover foods and liquids. You read it here first. And it’s tempting to thrown them into the dishwasher after you’ve emptied them of their original contents, label and all. Hey, you figure, this will get the jar clean make the label really easy to remove, right? The problem with this approach is that the label and glue will partially dissolve, sending paper pieces and glue into your dishwasher’s food filter, clogging it up and creating a messy cleanup scenario. Super-pro kitchen tip: remove labels first.
7. Anything Nonstick
Anyone who’s ever spent a half hour scouring burned food particles off a cast iron, steel, or aluminum pan knows nonstick cookware has its advantages. It’s so easy to clean! But for some people, “easy to clean” is not enough. They want something “effortless to clean,” so they throw their Teflon pans in the dishwasher. Just remember that Sloth was one of the seven deadly sins. In this case, “deadly” means you’ll kill your frying pan. After multiple washings, your pan’s nonstick coating will start to flake off. It will get into your food and give your intestines a nonstick coating. This is not good. Not to mention the fact that your pan will lose its nonstickiness.
Some nonstick pans are now marked as dishwasher safe. But unless your pan is clearly identified as such—or if you just don’t know if it is—don’t take the chance.
8. Anything Disposable
After an exhaustive internet search, we were unable to find any accounts of people who’d had the bright idea of washing paper plates in a dishwasher. Someone surely has tried this, but was probably too embarrassed to publicly admit it. We really don’t need to explain why this is not, to put it mildly, a good idea.
However, it’s not unheard of for people to put disposable aluminum pans in the dishwasher. This is not smart for two reasons. The pans themselves will come out with a mysterious black residue which science has yet to adequately explain. More seriously, the lightweight pans will rattle around while they’re being washed, leaving black marks on nearby dishes that are subsequently baked on and difficult to eradicate.
As for disposable cutlery, the danger is that the high heat and detergents will degrade the plastic, potentially releasing phthalates and BPA from the things you put into your mouth.
9. Anything Crystal
Crystal is cool and it doesn’t like the heat and detergents it encounters inside a dishwasher. It may become chipped, pitted, cracked, or cloudy. So that crystal punch bowl you only bring out for your annual New Year’s party? Ixnay on the ishwasherday.
10. Anything Gold
You’re at work and your husband texts you: “Emergency. Pls call.” You hastily excuse yourself from your annual salary review, duck into the hallway, and whip out your mobile phone. “What is it?” you ask frantically the moment he picks up. “I—I was doing the dishes,” he stammers out, “and all the gold washed off the good china and the gold-colored flatware looks yucky!” “You didn’t put them in the dishwasher, did you?” you ask. “Um, yes,” he replies. You immediately hit End Call and begin Googling divorce lawyers.
Yes, this can happen. Don’t let it happen to you. So when you buy a new dishwasher after visiting our 10 Best Dishwashers page, be sure you re-read this article. Twice.