Stoneware, porcelain, earthenware, terra cotta… what gives?

Sometimes the most basic thing to some is very confusing to others.  And how potters refer to the clay and firing temperature they use can be meaningless to the general public.  So what’s up with stoneware, earthenware, etc.?  Just what does that mean and why do you care?

Those terms define the type of clay used to make a piece of pottery, and implies the general firing range the piece was fired to.  Earthenware is fired comparatively low, for ceramics, anyway, at around 1700 degrees Fahrenheit.  The clay color may be orange, brown, beige, white, or just about any other color.  Usually there are other minerals in the clay that prevent it from being fired to higher temperatures.  Earthenware glazes are often very bright colors.  But the clay itself is still porous and won’t hold water unless glazed.  It is not suitable for the microwave or dishwasher. The orange flower pots are made of terra cotta, a type of earthenware high in iron… hence the orange color.  And we all know they are porous.

Stoneware is a clay that is formulated differently and fired to a higher temperature.  Usually around 2300 degrees Fahrenheit  It is much more durable than earthenware. .  For all practical purposes stoneware has fused and will hold water without being glazed. Practical purposes?  If one were to make a solid brick from the stoneware, let it dry and fire it, weigh it, boil it for 2 hours and then weigh it again, it should only pick up no more than 2% of it’s own weight.  That’s considered sealed. This makes it dishwasher safe and microwavable.  Like earthenware, stoneware can come in a variety of colors.

Porcelain is a pure white clay.  True porcelain is totally sealed.  If the wall is thin enough in a porcelain pot, it is translucent and light will show through it.  This takes temperatures in excess of 2400 degrees.

Although clay is natural and is constantly being produced by nature, it is rare to find one clay straight from the ground that has all the qualities a potter would look for in their clay.  So it is more common for clays to be mixed to achieve a clay body.  Adding some clays for density, some for plasticity, some for color, etc., is very common.