Porcelain, Stoneware, and China Dinnerware: Different Types of Ceramic Explained
If you're in the market for new restaurant dinnerware, you're likely to see different pieces described as "china," "porcelain," and maybe even "stoneware." You may have wondered about the differences between those materials and which would make the best restaurant dishes for your tables. This primer will explain what those terms mean and help you make the best choice for dressing up your dining room tables.
Ceramic is an umbrella term for the hard, durable, but relatively brittle substance that all traditional pottery and dinnerware is made from, no matter the specific process or the combination of ingredients used. All ceramic materials start with clay, which is comprised mostly of aluminum oxide, silicon dioxide, and water.
Other metals, like potassium oxide and iron oxide, may naturally be present depending on the type of clay in question, but manufacturers may add those and other minerals or substances to the clay mixture to give it the characteristics they want. Those additions are commonly called inclusions. Everything from the size of the clay's individual grains to its water content will have an impact on its physical characteristics, including its color, plasticity, porosity, and reaction to being fired. The combination of ingredients that go into a specific type of clay is called the clay body.
Individual ceramic pieces are formed from that mixture by hand or by machine into the desired shape, be it a plate, bowl, mug, platter, or any other type of ceramic dinnerware. Each piece then undergoes a series of firings in which it is exposed to temperatures well above 1,000 degrees Fahrenheit in a specialized oven called a kiln. That exposure to heat causes the clay to undergo a physical transformation that makes it rigid and durable.
Depending on the desired results, each ceramic piece will likely receive a coating of glaze before or between firings. Because many types of clay remain naturally porous even after they've been fired, that coating serves to seal the surface of the piece to prevent it from absorbing moisture from food and drinks. Manufacturers use a transparent glaze if they want the natural color of the fired clay to show through. More often, glazes turn opaque when they're fired and are chosen for the decorative colored finish that they give the final dinnerware.
Many types of ceramic are fired to temperatures high enough and held there long enough for the clay to become partially or fully vitrified. Vitrification is a process in which the ceramic is brought to its melting point. At that temperature, the clay and minerals fuse together and form a crystalline structure. The term is derived from the Latin "vitreum," which means glass, because the process gives the clay properties very similar to glass. The transformation strengthens the material dramatically and makes it much less porous than non-vitrified ceramics, sometimes so much so that manufacturers choose to forgo glazing ceramic pieces that have been fully vitrified.
ASTM International standards define the test that measures how porous a certain piece of ceramic is. The procedure generally involves immersing the ware in boiling water for several minutes, then soaking the piece in room-temperature water for several hours. The difference in the piece's dry and wet weights will help testers determine how much water it absorbed. A piece of ceramic's porosity will partially determine whether it's classified as earthenware, stoneware, or porcelain.
Porcelain vs. China vs. Stoneware
Different clay bodies and different firing procedures yield ceramics with different properties. Those physical characteristics determine the suitable applications, perceived quality, and value of each type. Here's a rundown of the three main types of ceramic you'll see in the kitchen or dining room.
Earthenware is the simplest type of ceramic available. Compared to other types, it's generally made with the least refined clay body and fired to the lowest temperatures in a process that's very similar to the ones employed by prehistoric humans to make the earliest examples of ceramics. That simple process yields wares that must be made relatively thick in order to remain durable. This type of ceramic is very porous, so manufacturers must cover it with a full coat of glaze if it is intended to hold food or liquid.
Terracotta pottery is a common example of earthenware ceramic. If you've ever dropped a terracotta pot, you know how fragile it can be and why it's not often used to present food. You're unlikely to find earthenware among a restaurant's collection unless it's being used to decorate the dining room, although residential dinnerware is sometimes made with glazed earthenware.
Stoneware is a step up from earthenware in terms of durability and is considerably less porous. Pieces made from this material can be made thinner and lighter, but must still be glazed to prevent the material from soaking up water. Virtually all restaurant dinnerware that isn't classified as porcelain is made of stoneware.
Stoneware provides a good middle-of-the-road balance between durability, weight, and price. It is fired into a vitreous or semi-vitreous state, and a stoneware piece tends to be a creamy or off-white color. If that is the desired finish of the final piece, manufacturers may apply a transparent glaze that lets that color shine through. Otherwise they may apply a colored glaze and any number of decorative decals.
The word "porcelain" is synonymous with the finest dinnerware that money can buy. That's because the material can be formed into the strongest, thinnest, and most elegant dinnerware available. The difference between porcelain and ceramic starts with its clay body. Porcelain differs from other types of ceramic with its inclusion of kaolin, a smooth, fine-grained clay that gets its name from a village in China where the practice of making porcelain developed. The combination of kaolin and inclusions such as alumina make porcelain strong enough that it can be formed in pieces so thin as to be transparent. It's that combination of delicacy and strength, along with its typically bright white color, that make porcelain ubiquitous on white tablecloths.
Traditional porcelain is often divided into two categories based on the clay body and procedure used to create it. The original Chinese version of the substance became known as hard paste because of the dense minerals used in its formulation. For decades, European manufacturers tried and failed to recreate the strength and elegance of true Chinese hard paste porcelain, and many resorted to using alternative formulations that took advantage of milder inclusions. Those mixtures became known collectively as soft paste.
Differentiating between hard paste and soft paste porcelain is now the work of antique china collectors. Commercial-grade porcelain is now made with materials and processes that make pieces incredibly durable compared even to the finest china produced in the past.
Bone china is a special type of porcelain made with a clay body that includes bone ash among its primary ingredients. In the United States, a clay body must contain at least 25 percent bone ash by weight to be classified as bone china, but other nations may have different definitions. The inclusion of bone in the clay body gives this type of porcelain its distinctive milky white and translucent appearance. It also helps makes the ceramic more durable by making it less brittle.
What is "China?"
Although the word "china" is often used generically to refer to all types of dinnerware, regardless of its quality or physical characteristics, most formal definitions include the quality of being partially or fully vitrified.
The United States International Trade Commission publishes official definitions of ceramic terms for tariff purposes. These definitions are based on the amount of water in proportion to a piece's weight that it will absorb when tested using the ASTM method described above.
- Both porcelain and china are defined as ceramic ware that will not absorb more than half a percent of its weight in water.
- Stoneware is defined as ceramic that will not absorb more than three percent of its weight in water.
- Earthenware will absorb more than three percent of its weight in water.