There are different types of earth used in Rookwood Pottery that are distinguished by hue, texture and resistance: earthenware, sandstone and porcelain. All are composed from the same material: clay. But there are many varieties of clay and according to their specifics, they are part of the composition of this or that ceramic paste.
These different ceramic pastes therefore each have a corresponding baking temperature. The faience is cooked around 1000 °, called low temperature cooking. It is a temperature sufficient to melt enamel without changing the characteristics of the body itself. Sandstone and porcelain cook around 1280 °, it is a high temperature cooking. The clay is vitrified, that is to say that it is transformed into a solid and non-porous mass.
The faience remains more or less porous after cooking. It is not very dense and light while the sandstone is denser and more compact. It remains relatively fragile and will break more easily in case of shock. Cooking at low temperatures makes it possible to develop enamels that are often brighter and more colorful than in sandstone.
If the dish is made with a cooking ground, the oven dishes will have good resistance to thermal shock.
Its slight porosity has the advantage of allowing some evaporation of liquids which can be interesting as for germoirs or flower pots for example. On the other hand, it often happens that these same flower pots peel or break when the absorbed water comes to freeze. They should be brought in or emptied in winter. In the same spirit, a place mat under a vase or a trivet under a pitcher will be welcome to avoid leaks and halos on the furniture.
Sandstone used in Rookwood Pottery is denser than earthenware because the earth has undergone a process of homogeneous fusion of all the particles of which earth is composed (like porcelain). It is said that the room is vitrified. Its strength and hardness make it possible to produce solid, everyday dishes that are resistant to scratches, corrosion and acidity (such as salt, vinegar, etc.).
The range of colors of sandstone is often darker than faience, because the colors do not all support the high temperature. That said, the techniques evolve and we see more and more colored sandstone.
After porcelain, sandstone is in second place in the production of high-temperature pottery, long considered nobler than low-temperature earth. Porcelain is a fine and translucent ceramic. It is a difficult land to work, the gestures must be precise and sure.
