Ceramics (cups, bowls plates, jugs, figures, etc) are divided into three major categories: stoneware, earthenware and porcelain. This column is a very quick identification guide to which of the three is that sports figurine in the antique store, football painted bowl in the estate stale or Kansas City Royals coffee cup your office desk. It is usually easy to make an identification, though there will always be some gray areas where it’s hard to tell if something falls into one or the other.
Porcelain, which has that signature refined, smooth, thin, ‘dainty tea cup’ look, is the only of the three categories that is translucent. This means if you hold up the item to the light you can see light come through it. If you pass your fingers between the item and the light, you will see the shadow of your finger pass by. Duly note that that this translucence is seen through only one layer of porcelain, such as with a cup or plate. Light usually won't shine through the multiple sides (front plus back) of a figurine.
Stoneware, which is opaque, tends to be heavy and substantial. It can look more basic, handmade and primitive— such as that old time country folk art jug. Anywhere the object is unglazed the clay is darker, usually dark grey but also sometimes light brown, often with dark specs in it. It has a rough texture, as it if was made out of a chunk of clay in middle school pottery shop. Stoneware cups, bowls, plates and similar usually have unglazed bottoms where you can see the rough, dark material. Due to being cooked at a higher temperature, stoneware can hold water even when unglazed—- thus the unglazed bottoms.
Earthenware, which is also opaque, is the most common form of ceramics. Most of your ‘department store’ dinner plates and coffee cups and mugs in your kitchen are earthenware. Unlike stoneware, earthenware is not waterproof when unglazed. This means earthenware is almost always glazed all over, including on the bottom. This is particularly true for a cup, bowl or jug that is intended to hold liquid. On an earthenware cup, plate or bowl the entire item will be glazed except for a thin white or off white rim at the bottom. That unglazed rim is the part where the item rested in the kiln. At this unglazed area, or any other glazed area such as a chip, the material is milky or chalky (unlike the coarse dark stoneware material).
Just remember that an earthenware cup, bowl or plate will be glazed on the bottom (except for the chalky rim), while heavy stoneware is unglazed on the bottom and has a darker, rough texture.
Terracotta is a type of earthenware that is common but looks distinctly different from other earthenware. Terracotta is usually a distinct orangish, but sometimes is a light brown/gray. The most common terracotta item is the orange flower pot.
As with all earthenware it is not water tight and must be glazed to hold water. As flower pots are meant to ‘breathe’ and let in and out water slowly, they are either totally unglazed or glazed only on the outsides. The outside glaze, usually in colors and designs, is for aesthetic purposes only. Flower pots also have a hole in the bottom to let in water for the plants.
There are terracotta figurines, often Asian, glazed in colors but with parts and the bottom unglazed. The unglazed areas will show the standard orange or light brown/gray terracotta color and texture. As stoneware is often brownish gray it can sometimes be difficult to tell whether a figurine is stoneware or terracotta. However, Terracotta figures are usually much more refined and smooth on the outside, while stoneware is more basic and folk art-style. Stoneware is also usually heavier.