Why Are Some Ceramic Mugs Not Dishwasher Safe?

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Ceramic mugs are commonplace in households, and like all other drinkware, they must be cleaned after use. But due to their composition, care should be taken when washing ceramic mugs to ensure they last you for years to come. 

Some ceramic mugs are not dishwasher safe due to the glazing process used. Specifically, low-fire glazes will erode with dishwasher use, while other glazes are harder and thus more durable. Always check the box or label provided before putting a ceramic mug in the dishwasher.

This article will help you determine if a ceramic mug is dishwasher safe or not and what ways a dishwasher may damage your ceramic mug.

How To Know if a Ceramic Mug Is Dishwasher Safe

Most commercially produced dishes are labeled with an emblem or phrase that specifies if the item is dishwasher safe or not. Luckily, even if your mug is not commercially produced or just without a label, there is a telltale sign to look for. 

The glaze is the determining factor. 

Low-fired ceramic mugs, which are typically colorful and decorative in nature, are not dishwasher safe. Therefore, if your ceramic mug is bright and colorful, it is best to avoid the dishwasher altogether. 

How Glazes Effect Ceramic

Ceramic glaze is a coating applied to an item, or in this case, a mug, rendering the mug waterproof and food-safe. 

Glaze is a powder made of three ingredients, although the proportions may vary depending on the type of glaze. These three ingredients are fluxes, glass formers, and stabilizers and are mixed with water to create a liquid suspension. 

The three different types of glaze include:

  • Gloss Glaze: This glaze produces a surface that is shiny and reflective.
  • Matte Glaze: Matte glaze surfaces are dull.
  • Satin Matte: This glaze is partially shiny on the surface.

Regardless of the type, glaze is almost always applied by either brushing, dipping, or pouring onto the ceramic ware.

After the application, it will need to dry completely, which could take several days. 

Next, the glaze is fired in either a low-fire, mid-fire, or high-fire. 

  • Low-fire glazes result in bright, predictable colors without much melting. 
  • Mid-fire glazes have more color variation and melt together. 
  • High-fire glazes have a limited color range.

If your ceramic mug was heated with a low-fire glaze, it will not be dishwasher safe. This is due to a lack of durability. 

Mid and high-fire glazes are generally more rigid and, therefore, usually safe for use in a dishwasher. However, it’s still best to check the labels if you have any. And if you’re in doubt, it’s best to stick to hand washing. 

Unglazed Ceramics Are Not Dishwasher Safe

Also known as bisque fired pottery, they’re fired and hardened, but this style of ceramic skips the glazing. 

Unglazed ceramics are porous, and some argue, not even food safe. 

Although it may not look it, and unglazed ceramics will hold water for a time, the clay is still porous, and it will eventually absorb that liquid. 

There are some other glaze alternatives, such as:

  • Metal leaf paint
  • Spray paint
  • Tempera paint
  • Varnish
  • Watercolors
  • Wax

While these may suffice authentically, they are neither waterproof nor food-safe. These alternatives must be sealed, and most chose masonry sealer or Modge Podge to do so. 

One caveat of unglazed ceramic mugs is the cleaning method. Soap cannot be used as it will affect the taste of your beverage, and they will not hold in a dishwasher. 

Instead, plain warm water or baking soda paste is used to clean. Because of this unusual cleaning method, most people do not use unglazed ceramics.

How Ceramic Mugs Get Damaged in a Dishwasher

Bear in mind that dishwasher-safe mugs and other dishwasher-safe dishes can also potentially suffer damage in the dishwasher. 

There is always the possibility of your ceramic mug getting cracked. For example, other items can bang against your ceramic item and crack or break it. 

Ornate mugs especially would probably fare best hand-washed. Soft ceramic mugs, which are both fragile and porous, should be hand-washed as well. 

As mentioned, an overly porous mug will absorb both the drink and dish shop, altering the taste of your beverages. 

Potential Damage Caused by the Wash Cycle

To understand how dishwashers can damage a ceramic mug, you should understand how dishwashers work. 

A washing cycle of a dishwasher follows these steps below:

  1. Adds water to a small basin at the bottom.
  2. Heats the water, usually around 155°F (68°C).
  3. Sprays jets of water to clean the dishes (This spray is quite forceful as food particles need to be filtered, chopped, and disintegrated). 
  4. Drains dirty water out.
  5. Sprays water to rinse the dishes.
  6. Drains again.
  7. Heats the air to dry the dishes.

While in the dishwasher, ceramic mugs and your other dishes go through extensive cleaning. Therefore, it must be durable enough to survive both the heat and high water pressure. 

Mugs that are not made of durable materials or have delicate designs can easily damage in a dishwasher. 

Some ceramic mugs are heat intolerant, and the heat from the dishwasher can break the coating of your mug. Damage can range from cracks and chips to breaks to designs melting off. 

Dishwasher Detergent

Another element of dishwasher cleaning that could potentially damage a ceramic mug is dishwasher detergent. 

As they’re designed to clean a large number of dishes with potentially days worth of dried-on foods, they need to be stronger than your average dish soap. 

These detergents can be harsh on a ceramic finish as most contain bleach and citric acid to combat water hardness and dissolve food. 

Other Dishes That Should Not Go in the Dishwasher

Ceramic mugs aren’t the only things prone to damage in a dishwasher. Here’s a list of a few other items you should only wash by hand:

  • Aluminum cookware. The dishwasher’s hot water can stain or dull the material.
  • Cast-iron skillets. The dishwasher can break the coating, and rust may occur over time.
  • Chef’s knives. The blades may dull over time.
  • Copperware. The dishwasher can tarnish these stylish dishes over time.
  • Fine china and crystal. These delicate dishes should never go into the dishwasher.
  • Insulated cups and mugs. Water can seep into the insulated area.
  • Milk glass. These retro glasses can end up with a yellow appearance after a trip through the dishwasher.
  • Nonstick skillets and sheets. Some are dishwasher safe, but for others, the nonstick coating can degrade after dishwasher uses.
  • Pressure cooker lids. The high temperatures could warp the rubber seal or damage the valves and vents. If your pressure cooker cannot properly seal and vent, you may experience a pressure cooker explosion.  
  • Soft Plastics. Sturdy plastics are acceptable in the dishwasher, but softer plastics can warp.
  • Wooden utensils and cutting boards. Again, the hot water is the culprit, causing the items to warp or crack once dry. 

Is My Ceramic Mug Microwave Safe?

Most ceramic mugs are microwave safe, but it is essential to check for a label to be sure. Ceramic absorbs heat, so after even just a minute, the mug will likely be very hot to the touch. For lesser or low-fired ceramic mugs, the more you heat them, the higher the chances are they will break.