Differences in Ceramics, Glass, Pottery, and China[retrieved from http://www.cajunc.com/art-ceramics-differences]
Ceramics and its categories include some words you might not expect. Although you may think of ceramics as art, ceramics includes brick, glass, tile and toilets along with pottery, earthenware and stoneware. Forming ceramics requires clay or sand combined with other ingredients and heat.
Glass is made from natural products like soda ash and silica sand heated to a high temperature. Some companies use recycled glass as part of the mix.
Intense heat changes the glass into a molten state so man or machine can form a useful piece for art or commercial product. The liquid glass is blown, molded or both.
Hand worked glass is mouth blown but may be blown into a mold.
- A gatherer removes molten glass from the hot furnace for pressed glass.
- The gatherer places the correct amount of molten glass into the heated mold.
- The mold creates the shape and it's opened while the glass is still hot.
- The glass hardens as it cools. Quality glass is fire-polished so the seams don't show as much and the surface is shiny.
- The annealing process allows the glass to cool slowly to avoid breakage. The surface and interior temperature of the glass is kept nearly equal to reduce strain on the glass. To learn more about annealing, see Corning Museum of Glass: Annealing Glass.
Glass can be any color, even opaque. Cambridge glass is often opaque, with color names like crown Tuscan and helio. Milk glass and black amethyst are collectible opaque colors in vintage glass.
For more information on the process of glass manufacturing (or if you happen to be in the Cambridge, Ohio and want to tour their facility), see Mosser Glass, Inc.: Process.
Pottery includes earthenware, stoneware and everything in between but the distinction between the different names is in the firing temperature.
Pottery is made from clay and unlike glass, is opaque even without coloring. Studio artisans make pottery on a potter's wheel with clay selected from the area or shipped in a bag. Mixing water with the clay makes it malleable and the potter's skill makes it beautiful.
Whether commercial production or studio pottery, the composition and color of the clay makes a difference in the weight and color of the completed piece.
Although the potter glazes the surface, a red-clay body with a heavy white glaze will still show the dark body through the glaze. A good example is visible in the 1972 Frankoma Easter plates. Some of these plates are red clay and show a brownish tinge with the white glaze; others are white clay and look stark white with the glaze. You can see the white glaze over red clay in the 1970 Christmas card (right).
Earthenware is often red clay called red ware and is low-fired pottery.
Some earthenware is hand-formed without a potter's wheel. Some Native American and artisan potters roll clay into coils to make hand-formed vessels from spiral coils of clay. For some more information on Coil Pottery, see: Brothers Handmade: Coil Pottery.
Pots can be sun baked. You may have made these as a child, and they aren't as strong as pots baked in a kiln.
Red clay has a high iron oxide content, and Georgia and North Carolina are two states with abundant red clay deposits. For more information on Georgia soil and clay, the USDA Natural Resources Conservation Service has an article "Why are Georgia Soils Red?".
Yellow ware is also earthenware. You guessed it – it's made of yellow clay.
Yellow clay can typically withstand higher firing temperatures than red clay, making a sturdier product.
Yellow ware glaze is usually clear, and early yellow ware was undecorated or decorated with rings, called banded ware.
After banded ware decorations, makers used molds with raised decoration, then mocha and Rockingham glazes on the yellow clay body.
Mocha decoration was spinning designs between the bands, giving the appearance of seaweed or an earthworm. Rockingham looks like tortoise shell created by dripping manganese onto the yellow body.
Bennington, Vermont produced yellow ware with Rockingham glaze, often called Bennington ware.
Ohio had available yellow clay and became the center of yellow ware production in the United States from about 1840 to 1870.
Lisa McAllister's Collector's Guide to Yellow Ware: Book I; An Identification & Value Guide provides good information about yellowware and the yellowware production with around 300 photos and prices, updated in 2003.
If red ware is red clay and yellow ware is yellow clay, what is greenware?
Greenware is the unfired clay, so it can be very wet and just off the potter's wheel or out of the potter's hands.
Depending on the size and thickness of the piece, it takes a week or two to dry. After drying, the greenware can be used for dry objects, but if you add water, you're back to clay again.
Water soaks through greenware. Some artisans wait until the greenware is sufficiently dried to carve or make sgraffito designs for decoration.
The bisque firing, or the first kiln processing, turns the greenware into pottery, making it durable and resilient. The firing temperature determines the durability of the ceramic body.
Finer clay and higher temperature for firing makes porcelain different from pottery -- although it's more difficult to tell the difference with some pieces than others.
Kaolin, quartz and feldspar make the porcelain body and a glaze that withstands high temperatures makes the product non-porous.
Porcelain is hard-paste or soft-paste.
- Soft-paste feels sandy where it's chipped
- Hard-paste is shiny and vitrified.
Collectors Weekly: Flashback: Identifying China By Its Paste is a good article for more information about porcelain paste and variations of china and porcelain throughout history.
You can also hear the difference when you flick it with your fingernail.
Collector plates are often porcelain and some are bone china. Lenox, Flintridge, Franciscan, Gorham, Castleton and Syracuse made fine porcelain dinnerware in the U.S.
You may have heard "china" used to describe porcelain dinnerware. The country of China was the original source of porcelain, but "china" usually refers to bone china.
England was the source of much of the bone china in the U.S. This product has bone ash or animal bone, kaolin clay and feldspar or china stone. Bone china is usually thin enough that you can hold it to the light and see your hand through it.
The difference in bone china and vitrified china is in the products used for the body.
- Bone china base products are combined with water and sent through a filter to assure fine quality without lumps or clumps.
- The water is removed and the pieces are shaped and fired at a high temperature.
- Decorating and glazing are the last steps in creating a piece of bone china dinnerware.
Using a fragile product like china or porcelain to make utilitarian articles such as bathroom fixtures is done with the high firing temperature of vitrified china.
Your commode and bathroom sink may be vitreous china. This is a high-fired ceramic that almost feels like glass.
Vitrified china glaze becomes glass-like and part of the core product because of the high firing temperature, causing crystals to form within the glaze to seal the piece.
The American National Standards Institute (ANSI A137.1) tests resistance to water for ceramic tiles, and rates them as non-vitreous, semi-vitreous, vitreous and impervious. Soaking in water proves the vitreous qualities.
Non-vitreous ceramics may absorb more than 7% of the water by volume, while semi-vitreous is between 3-7%. Vitreous china absorbs between 0.5% and 3%, and impervious is one-half percent or less, according to the ANSI tests.
For more information on the vitrification process and ceramics (specifically tiles), see StarCraft Custom Builders: Porcelain or Ceramic Tile – What Is The Difference?.
Companies used vitreous china for the nearly indestructible restaurant ware of the 1930s through the 1960s, made by Syracuse, Walker, Buffalo, Alamo, Onondaga, Iroquois and others.
Hotel china and railroad china were common forms of restaurant ware or vitreous china, decorated with advertising for the restaurant, hotel or for the railroad.
Stoneware is another ceramic product, usually made with an inexpensive dense body that is semi-vitreous or vitreous.
It is denser and stronger than earthenware, thicker than most of the other ceramics.
You may think of stoneware as crockery, but fine stoneware may be art pottery with careful selection of the raw materials.
Stoneware is made of clay, quartz and feldspar and can be hand-turned on a potter's wheel.
Sometimes you can identify stoneware by the gray color, but stoneware can be any color the maker chooses.
Red Wing, Texas Star, and Louisville Stoneware all produce stoneware in the United States today, but almost every state had stoneware production a century ago. These companies made pickle crocks and water coolers and all kinds of utilitarian pots in stoneware.
Red Wing Stoneware is still in operation today. For more about their history and products, see Red Wing Stoneware Company.
Companies use hydrostone, ferrostone or other manmade products for production of figurines and knick-knacks today in the United States.
Red Mill Manufacturing (often seen as Red Mill Mfg.) uses pecan shells combined with other products to form figurines.
Foreign imports use resins for many of the popular figurines at the local dollar store.
These products aren't ceramics in the narrow use of the word, but perform like ceramics in the creation of figurines. One way you can identify these products is that they are usually solid, not hollow like porcelain or pottery figurines.