There is all kinds of best practices for stacking and loading dishes, and what to put in a dishwasher. Let it be known, though, that there are some things a dishwasher can really mess up.
Don't put knives in the dishwasher
It's true. Dishwashers dull knives. I cannot believe that I am the age I am and never knew that. Even my husband, a knife connoisseur, didn't know that. Geez.
Knives lose sharpness in a dishwasher due to damage from high temperature, moisture, motion damage, and corrosive detergent. The culmination of the activity of washing results in a dull knife.
Detergents have been known to discolor knife blades. They're not all that kind to the integrity of the blade, either. "Motion damage" means that knives, when interspersed among dishes, will hit the dishes when knocked by jets of water. The bumping into other items is what dulls the knives.
Not only do knives hit other dishes, they hit the frame of the dish rack itself. The dishracks are coated with plastic - not friendly to keeping sharp knives sharp.
Finally, the temperatures and moisture can mess with the steel and handle, where the handle meets the steel blade. This is especially true of wood handles. High heat and moisture can loosen wood, warp, and even crack it. If the wood is connected with pins, it can weaken the connection point with that too.
Especially at risk are ceramic knives. If you have ever handled a ceramic knife, it's wild - they feel like you are cutting with glass. These knives are at greater risk, because they are so brittle. There are reports of these knives actually breaking in two in a dishwasher!
All of these micro-abuses wear knives down, resulting in knives losing sharpness.
In the above picture, knife abuse is reduced by putting on a separate top rack where each knife can be separated from knocking against other dishes, good! The picture also shows a knife with a wooden handle put in the dishwasher, bad! Dishware comprised of wood should not be put in dishwasher.
I wouldn't say that dishwashers ruin knives, they can be re-sharpened. However, every time you have to re-sharpen a knife, you are shortening the lifespan of the knife. I haven't totally screwed everything up with my cutlery. My husband and I have very rigid rules regarding our RADA cutlery. Those never go in the dishwasher!
Avoid putting stickers and labels in dishwasher
Bottles or dishes with stickers or cans with paper labels should not be put in the dishwasher. The paper can wash off and be sucked through the holes of the dishwasher blade arms. Label quality varies, such as heavy-duty vinyl vs. stickers for fun.
Printable water-proof labels for glass, plastic, wine bottles, bottles, etc. can be purchased and printed off a home printer. This is what some do-it-yourselfers buy and use to apply to bottle projects made in their home. The quality and sticker life is likely short for these products.
I touch on specific use-case scenarios below that people want to know more about.
Wine bottle with stickers in dishwasher
A wine bottle with a heavy-duty vinyl label or sticker with a plastic feel could be put in the dishwasher. If the label feels more papery, it will have a higher chance of washing off in the dishwasher.
Why people would put a wine bottle in the dishwasher, I have no idea. Just rinse it out under the kitchen sink faucet and place in your recycle bin.
Water bottle with stickers in dishwasher
Fun stickers or vanity stickers for water bottles, cell phones, laptops, etc. are a popular thing among kids. My daughter's laptop is plastered with them. It's a fun way to be unique and stand out, or show your passion for your fan favorites.
Although water bottle stickers or vinyl stickers are advertised as dishwasher safe, some consumers report that the labels fade and come off in the dishwasher.
All Hydro Flask powder coated bottles are dishwasher safe. If you wash a Hydroflask bottle with stickers on in the dishwasher, the stickers may come off, depending on the quality of the sticker material and adhesive. Hand washing a Hydro flask bottle with stickers is recommended.
Not all Hydro Flask products are dishwasher safe. The Hydro Flask Coffee Mugs are not powder coated, and they are not dishwasher safe. Refer to the Hydro Flask website for more information.
Stickers on water bottles don't last. Sticker life varies greatly depending on the sticker material and adhesive. Everyday use can scratch or lift up the sticker, weakening it and shortening the sticker life.
If bottle labels are intended for the dishwasher, they should be fine, but you don't really know if they are. For example, if you have a Hydroflask plastered with stickers, it's not going to fair well. Vanity or stickers for fun are not
Dishwasher safe identification labels
Some identification labels are designed to go through a dishwasher. A perfect example of this are kid's dishwasher safe labels to identify their lunch containers and water bottles in daycare or at school. Or maybe the adult in the family wants to mark their dishes for work.
From the dishwasher safe labels I looked at, folks were very satisfied for the product. Some people put it on clothing, even though the description said it wasn't made for clothing - those were the only people disappointed.
Still, not all labels are forever. Label life varies depending on the quality of the paper used (it definitely needs to be water proof) and the adhesive type. You may fair well for the first few washes, and then it goes downhill from there.
As with the water bottles, stickers and labels can weaken over time. The label can get scratched or lifted up, introducing a path for water to enter and start eroding away the grip of the sticker on the dishware.
Canned food labels in dishwasher
I've seen people take an empty metal can with label on and put it through a dishwasher. The reasoning is to clean the can and then place it into the recycling bin. This will always result in dishwasher disaster.
Labels for tin cans only have adhesive on one spot or strip on the can. The rest of the label is not glued down. It will easily lift off of the can and be beat up by the spinning dishwasher arms.
In addition, the paper will be flushed down into the drain and the dishwashers mini garbage disposal. Unfortunately, bits of paper will also be caught up into the nozzle holes of the spray arms and get stuck. I discuss trying to remove these bits in When Good Dishwashers Behave Bad. By all means, never wash metal cans with labels in a dishwasher!
Insulated travel mugs; AirBake cookie sheets are not dishwasher friendly
Any product with a layer between layers will take on water. I found this out with my AirBake cookie sheet. I could hear the swishing of water inside after I took it out of the dishwasher. The water doesn't come out either. Over time, it does evaporate, but it is slightly annoying to deal with. When I wash my AirBake pans, I hand wash them as quickly as I can in the kitchen sink.
This is completely from personal experience, I could not find anything on an official AirBake website to dig further into AirBake sheets and dishwashers. However, I did find this information stated on an Amazon listing for an AirBake,
"AirBake is designed to breathe and is not watertight. However, AirBake is dishwasher safe. DO NOT USE DISHWASHER DETERGENT TABS - the concentrated cleaning agents will damage the bakeware's finish. DO NOT SOAK - if water is inside pan layer, there is a risk of burning from steam release. If your pan has water inside the two sheets, place the pan upside down in a 250-degree oven for 30 minutes or until water is removed."
Likely, care instructions for the AirBake are provided on the packaging when you buy it. It's a good point about the steam release, because that is exactly what happens when the pan goes into the oven, it is released as steam. Thus, the companies recommendation on how to remove the water.
I've heard of the travel mug woes through conversation, but it is the same issue. According to Cascade Dish Washing Detergent, "Putting your favorite travel mug into the dishwasher may ruin its vacuum seal and ability to retain heat."
Wood hates dishwashers
The heat and humidity inside dishwashers can cause wooden kitchen utensils, such as wooden cutting boards and wooden spoons, to warp and crack.
From the perspective of a woodworker, my father-in-law explains how the hot water can loosen the adhesive of joined or glued boards. Any utensils with a wood handle or all-wood utensils (like wooden spoon or bamboo scraper) should not go into the dishwasher in my house. This also includes wooden bowls, cutting boards, and wood rolling pins.
Homemade art products, painted terra cotta, home made clay art should be hand washed
Those precious art projects made by your kindergartner will not survive the dishwasher. The acrylic paint isn't made for it. If you want to preserve the memory, wash or wipe the surfaces lightly by hand. Use the gentlest soap available. Any abrasion could slough off the paint - do not immerse in water.
Dishwashers have the potential to destroy your work of art. The wash cycle will remove the paint leaving you with a partial design, scratched off, or deformed and unrecognizable art piece. If it's important to you, don't put it in the dishwasher!