When you go for your first pottery throwing lessons your potter-teacher will have made the most suitable choice of clay for you. However, if pottery making is going to become an important hobby for you (or perhaps turn into a business) you will need to know about clay. The key question is: how do I know what clay to choose for my pottery throwing, pottery hand-building projects, tableware and sculpting? The answer is not difficult when you understand a little about the various types of clay that you need to take into consideration. Let’s get into it.
Your choice of clay is largely determined by the process you are going to embark on. For example, you might be making a coil pot, or you might be throwing at the wheel. Additionally, you will want to also take into account the required firing temperature and the finish on the pots that you want to achieve.
There are unlimited types of clay but largely we place them in 3 categories: earthenware, stoneware and porcelain. These 3 categories of clay types are distinguished by their firing temperatures.
Earthenware is fired to 1060 – 1130 degrees centigrade and has the lowest required firing.
Stoneware is fired to 1240 – 1280 degrees centigrade.
Porcelain is fired to 1280-1300 degrees centigrade and has the highest temperature requirement of the 3.
Please note that if you are a beginner at pottery, you should discount working with porcelain as it is an expensive material to purchase with the highest firing costs. Also, beginners find porcelain difficult to work with because it becomes soft quickly and collapses easily. So, steer clear of porcelain until you become more experienced.
Now that you know the firing temperatures how will you know which type of material is best for your current project? In order to narrow your choices, consider the way in which you will be producing your ceramics.
Throwing on the wheel and hand-building with clay
Most earthenware is the ideal clay for throwing on the wheel and hand-building pottery. You will find that earthenware is highly malleable which makes it easy to use. Also, its porosity is ideal for flowerpots and other constructions that are usually left outside that are required to breath. Basically, anything can be made with earthenware. It can be made watertight, and safe for food storage by glazing it. Remember, the final piece should not be put in the dish-washer; hand wash only.
As mentioned above, as earthenware is a low-fired clay, it is more economical which is always an important consideration for the potter. Most earthenware is bisque fired to 1000 degrees C and then glaze fired.
You will recognise earthenware often by its distinctive colour which is typically red or orange. However, it can also be found in white. The white clay should be considered a throwing clay only, due to its higher shrinkage.
Dinnerware and mugs
As they become more proficient, most potters at some point decide to try their hand at making dinnerware, plates and bowls, and drinking vessels such as mugs. It is very satisfying to be able to showcase your throwing skills in the form of a complete dinner service for when your dinner guests come round! When you reach this stage, you will probably choose stoneware clay for this type of pottery.
The reason for this choice is that stoneware is much more durable than earthenware and therefore, more chip resistant. No one wants to eat from chipped plates!
Most potters really enjoy the experience of working with stoneware as it can be, like earthenware, highly malleable and as beginners we tend to have to play with our clay for longer than the more experienced potter, so it works well.
The traditional stoneware glaze firing temperature is 1240-1280 degrees C, the higher temperature gives a more mature feel to the finished work. More recently mid-fire range has become popular typically at Cone 5 to Cone 6 at 1180-1200 degrees C. When choosing your stoneware clay it is imperative that you know its maturing temperature.
Creating Sculpture for outside.
Stoneware clay is one of the most popular materials to use for sculpting today. When you find a clay that you want to use for sculpting, one of the most important qualities to consider is its finished look (especially if you would like to emulate stone and not glaze it). The texture of the clay is another important consideration; many stonewares will contain an additive called grog which not only provides a more open texture, it will also be more forgiving during the hand making process. The addition of grog also renders the finished piece more durable in seasonal and weather changes.
It is advisable to always test the clay for its viability before you purchase it in bulk. In order to test the clay simply form a coil/sausage with the clay, approximately 10 cms in length and 1cm in diameter. Bend the clay to see if any cracks in the clay appear. This will demonstrate the materials textural and plastic qualities.
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