A ware that absorbs water can break inside a microwave. This is because the water in the clay expands and turns to steam. Pieces that are to be used in a microwave should be vitreous, which means they no longer absorb water. Another reason is uneven heating.
What you're seeing there is unintentional crazing. It's fairly common for this to appear at the first time you use it with a hot liquid, or microwave it. What's happened is that the glaze is 1% smaller than the clay body, so the first time it heats and cools, it crackles.
Ceramic plates are porous, and I would agree with BatamBasher135 - the plate was not 100% dry and had moisture inside the plate which reacted to the microwaves and caused the plate to crack.
The problem of too hot ceramic dishes from the microwave is due to metal molecules in the glazes and sometimes in the clay. Clays are composed mainly of the mineral feldspar and so are glazes. Pure clay will not be appreciably heated by microwaves.
Cracking is mainly caused by uneven drying of the piece, meaning that some parts of the pottery shrink more than others. The key to avoiding these pitfalls is to create a consistent environment for drying the piece and undertaking the necessary preparation to ensure that the entire piece dries at a similar rate.
Crazing is the effect on pottery which causes it to have a web of tiny cracks over its surface. These are not cracks in the actual structure of the pottery but actually an effect on the glazed part of the pottery.
Sudden changes in temperature cause localized thermal expansion, this produces tension and compression that easily cracks most ceramics.
In most cases, ceramic cookware is fine in the microwave. The only exception comes when it is lined or rimmed with metal.
Glass, paper, ceramic, or plastic containers are used in microwave cooking because microwaves pass through these materials.
Check the material is Glass and ceramic are usually safe. Avoid metal mugs. test: Fill the mug with water and microwave for 30 seconds. If the mug is hot but the water is cold, it's not microwave safe.
GE Appliances recently came out with a statement saying extreme heat from popcorn bags is the primary cause of microwave plates breaking. The superheated oil in popcorn bags, when in direct contact with the glass, can create stress points prone to fracturing.
During drying clays and porcelains shrink as they become rigid. When this occurs unevenly, cracks are the result.
Empty mugs: For one reason or another, if you're thinking about microwaving an empty mug, we highly advise that you don't. Since there's no liquid to absorb the microwaves, the mug will become excessively hot and start to crack.
If there is a hole in the microwave interior, we recommend that the microwave be replaced. Minor chips to the surface coating on the microwave's interior cavity will not affect the product's performance.
It's possible to distinguish between cracking and crazing by pattern (crazing manifests in mostly parallel rows, while cracked paint has a "checkerboard" appearance), whether paint has attached firmly (crazed paint usually achieves firm adhesion) and whether paint is flexible or brittle (crazing can occur in soft paint ...
Crazing is often seen as an interesting visual element, but from a food safety point of view, crazed ware is unacceptable. Crazing can severely weaken a piece and provide space where water can enter and saturate the clay if it's not completely vitrified. The cracks may also harbor bacteria if not sanitized regularly.
Anything made of or containing steel, iron, copper or other hard metals should never go in your microwave. Metal surfaces reflect microwaves, which increases the heat inside the appliance and could lead to a fire.
Microwaves will pass through glass, paper, and ceramic objects, making them the preferred materials for microwave-safe cooking. However, microwaves do not pass through metal, making it problematic for the appliance.
Most ceramic, china and earthenware dishware like porcelain plates and bisque figures are A-okay for microwaving. To test ceramics, microwave them with some water for 30 seconds. If it feels way hotter than the water, it's problematic.
Well, whether or not ceramic bowls can be used in the microwave actually depends on the type of bowl. This is because there are some types of porcelain and stoneware that are not suitable for microwaving since they are too delicate to deal with high heat. However, some ceramics are microwave-safe, but not all of them.
For our recommendations, we stick to stainless steel, cast iron, and enamel or ceramic coatings. If you're making the switch from traditional nonstick cookware, you should look into ceramic or enameled cookware. These coatings tend to hold up for years, especially if you cook over medium to low heat.
Glass-ceramic ware and heatproof glass ware are safe in the microwave oven. Oven cooking bags, baskets made of straw and wood (without metal), wax paper, parchment paper, and vented plastic bags are all safe to use in the microwave. Paper products that are specifically approved for microwave cooking are safe to use.
Both tiles are made from a clay mixture that's fired in a kiln, but porcelain tile is made from more refined clay and it's fired at higher temperatures. This makes it denser and more durable than ceramic tile.
Understanding the Fundamentals of Kiln Explosions
As the kiln temperature rises, any residual moisture in the clay begins to evaporate, turning into steam. If this steam is trapped within the clay body due to insufficient drying or improper venting, the increasing pressure can cause the pottery to fracture violently.