A good brick earth can easily be moulded  and dried without cracking and warping.

A good brick earth should have the following composition:

1. Alumina or clay 20 to 30 percent by weight.
2. Silica or sand 35 to 50 percent by weight
3. Silt 20 to 35 percent weight.
4. Remaining ingredients which include : Lime (cao) , Oxide of iron ,Manganese oxide , Manganese , Sodium potash etc.                  1 to 2 percent by weight

Alumina :

It is the principal constituent of every kind of brick earth. A good brick earth should contain about 20 percent to 30 percent of alumina.

It imparts plasticity to the brick earth, which is essential for proper moulding of bricks alumina or clay in brick earth shrinks and cracks on drying. It also warps and becomes very hard on burning unless mixed with sand.

Silica :

A good brick earth should contain about 50 percent to 60 percent of silica. Sand alone is in fusible but it fuses in the presence of lime and oxides of iron at kiln temperature.

Sand or silica in brick earth prevents the shrinkage, cracking and warping of bricks. It also makes the bricks durable. Excess of silica makes the bricks brittle and weak.

Lime :

A small quantity of lime not exceeding 5 percent is desirable in good brick earth.

It helps to bind the particles  of brick earth together. It also reduces shrinkage of bricks.

Oxide of Iron :

A small quantity of oxide of iron to the extent of about 5 to 6 percent is desirable in good brick earth and binds the particles of clay together.

It also provides the required red colour to the bricks on burning but excess of oxide of iron makes the bricks dark blue.

Magnesia :

Small quantities of magnesia in bricks of yellowish colour and reduce shrinkage. But excess of magnesia leads to the decay of bricks.

Manganese :

The presence of manganese in small quantity in brick earth makes the bricks darker or even black.