Ceramics have been around for countless centuries. They have been used in an incredibly infinite variety of items, ranging from the common cups and plates used today, to ancient record keeping in early Mesopotamia thousands of years ago. 

Ceramics are considered to be inorganic nonmetallic solids. The earliest known ceramic pieces found are over 27,000 years old. Creating a basic ceramic item follows the same concepts used for thousands of years, not changing to this very day. Simply clay is molded into a shape and dried slowly to remove all water to help prevent cracking. It is put into a high-temperature fire or kiln for about 20 hours at 1,500 degrees until the clay almost hits its melting point. At this point, the fire or kiln temperature will slowly be lowered over an additional four-five hour, to a point where the temperature reaches a temperature for handling. The reason for lowering the temperature slowly is that once the ceramics have been fired and the ceramic item is then exposed to the cooler surrounding air, the temperature difference is enough to crack the ceramic and possibly make it explode. Once the clay is fired it is then called greenware. This greenware can then be glazed and fired again. Greenware is much more durable than unfired clay but it is much more prone to shattering like glass. 

One of the most important parts of ceramics is not just how the clay is fired and cooled, but the types of clay used in the process of preparing the clay for firing. Clay comes in many varieties and combinations but there are three main varieties, white, red (which contains rust), and black volcanic clay. White clay is the most common form used. Mainly from my own experience, I think it is used because it does not stain clothing as easily as red clay.  However, red clay is also popular. It contains a lot of rust. The rust gives it, its unique red color. This rust coloring can also permanently stain clothing. Black volcanic clay is more expensive because it contains volcanic ash which is more difficult to obtain. It is mainly used as a pigment to darken the clay. Sometimes it is used as slip (liquidity clay) for creating a thin layer of black clay on top of white or red clay. Any of these types of clays can be mixed to create unique artwork. When creating ceramics, the number one thing that cannot be inside unfired clay while it is being made is air pockets. Air pockets if present, from carelessly untreated clay, when fired can cause slight temperature differences. The expansion of the air inside of the air pocket can result in the ceramic becoming unstable causing shattering or an explosion. 

The purity of the clay is another essential factor when creating a ceramic item. Clay for the most part when fired allows an artist to incorporate organic items that can be burned away. Items such as twigs and sticks. Metal wire can be put inside the clay to give a texture to the clay or as a support structure for thin pieces. Some materials you may not think would damage a ceramic while being in a kiln may cause problems. For example, any material containing limestone such as plaster is one of these problem areas. If by chance plaster accidentally gets introduced into a piece of clay while wet, and gets fired the limestone will react to the heat. The limestone intensifies the heat in the area where it is located and then explodes with the intense heat. While limestone is used for making steel because it helps remove carbon from the iron, in ceramics limestone can be catastrophic because even a tiny amount is enough to shatter a hot unstable ceramic. 

Glazing Ceramics

Once a person has made an item out of clay and had it fired once, to create a greenware ceramic, then it can be glazed. There are several types of clay originating in Egypt having unique natural mineral salts within them. When fired those salts melt and coat the outside of the clay object and react with the heat, creating a highly prized royal blue glaze. Unfortunately due to the salts within the clay, making anything with the clay is limited to very small items such as beads or jewelry. This type of clay is not suitable for functional items such as vases or bowls. When fired the clay becomes gelatinous and can easily melt and collapse, under its weight in the kiln. This type of clay does not need to be glazed. 

Standard white, red, and black clays can be glazed to make them more durable and stronger, allowing them more suitable for eating or for decorative uses. Glazes come in a wide variety of colors and textures and all use the same elements of glass making. In ancient days lead was common in many glazes as well as glass which was toxic but was used for decorative purposes.

Clear glaze which mainly consists of powdered white sand, is ground into fine a powder and mixed with water and adhered to the greenware ceramic surface. The greenware is then fired again. This allows for ceramics to be made for kitchen or dining household items.  To add color to the glaze a common technique used is to use a colored glaze and cover it with several layers of clear glaze which allows the color show through but not the toxicity of the colored glazes. Just like making greenware, when ceramics are fired again the glaze must be cooled slowly after firing otherwise the temperature differences will shatter the ceramic as well as the glaze upon the ceramic. When fired as you can imagine the glaze melts becoming a liquid. All the particles of glaze melt together to become a coating of glass. This coating of glaze must be put on carefully. If the glaze is put on too thin the glass will not stick to the ceramic; if put on too thick the glass will begin to drip off; if done just right the glaze will melt staying relatively close to the same spot where it was applied originally.

  There are other types of decorative glazes found that actually react to the air when cooled. The glaze will react to the air and change color similar to an oil slick upon water. The glaze will change color depending on the moisture content of the air. Once this change happens to the glass it becomes permanent. 

Some other special types of clay found in China eventually became known as bone china. The unique clay from China, when fired becomes opaque and translucent and is prized. It consists of a special type of quartz making the ceramic opaque, and light can go through it unlike regular clays. Bone China is different from other ceramics because the clay particles are so fine it is capable of being made into very thin items. Bowls and plates made out of Bone China, when clinked can give off a ringing noise. In ancient times people lightly tapped the china to see if it rung and if it did, it meant they would have good luck as well as proving it was the real deal, not an imitation. Decorating Bone China uses different processes. The glazes used are put on before it is fired into a greenware state, eliminating the need for extra coatings of clear glaze.