The types of clay used in pottery, called terracotta

The types of clay used in pottery, called terracotta (baked clay), have common characteristics:

- Red or yellow.
- Porous due to their high component of iron and other mineral impurities.
- Composed of fine-grain pasta and high plasticity.

- Cooked at low temperature between 950 ° and 1100 ª C.

When we draw, this type of clay, the tank or natural reefs, has a reddish color, tending to brown, green or gray due to the greater or lesser presence of iron oxide. After the first firing or (bisque) color varies.

The clays best known of this group are:

The red clay color named after her, both when wet and once cooked, because of its high iron content.
In nature we find large quantities of this type of clay, often at ground level, although in many cases, in their natural state, it is a very plastic clay, and contains many natural impurities and sediments, by what needs to be put to a washed and decanted into reservoirs used for this purpose.

It may be that in the process of sedimentation, many calcite have been deposited or soluble alkaline salts which would make it unusable in a paste for ceramics.

The blue clay, also belongs to this group called blue for its high lime content, but once cooked turns a yellowish color.
In its natural state has a grayish blue color, no doubt, is the most plastic of all pulp. After the first firing changes its color to yellow.
Most of the potters reject this type of pasta, although some use a mixture of the two and, if the mixing does not mix too, to cook, presents some interesting colors, but has the disadvantage of the break.