I’ll tell you a secret. Some other manufacturers may add barium sulfate such as the sanitary ware manufacturers that manufacture your bathroom fixtures. Some potters add it too.

Vanadium compounds cause scumming in otherwise pretty white bricks.

D

Brick manufacturers usually mine clay by the open pit method. That means that they usually don’t tunnel for the clay. They carefully remove the overburden (the dirt, weeds, trees, old cars, and what-have-you on top) leaving a clean clay or shale face. Then they mine the clay or shale and deliver it to the factory.

At the factory, it is crushed or ground as required, water is mixed in, and the clay is extruded by means of an auger into a very long rectangular cross section that is cut into brick as it moves along the conveyer belt.

Now days, everything is automatic in most plants including the loading and unloading of bricks into and out of the kiln. (See Ceramics: Industrial Processing & Testing, John T. Jones & M. F. Berard, Iowa State University Press)

In other words, brick manufactures have a one component composition (the clay or shale). Now there is always an exception. Clays and shales happen to have some sulfate content. This is not good. You might get blistering or scumming or some other unpleasant defect.

What do they do?

They add barium carbonate or some other chemical to tie up the sulfates because barium forms insoluble sulfates. These materials are not premixed into the clay. They are just sprinkled on the clay and the extruder does sufficient mixing.

I’ll tell you a secret. Some other manufacturers may add barium sulfate such as the sanitary ware manufacturers that manufacture your bathroom fixtures. Some potters add it too.

Vanadium compounds cause scumming in otherwise pretty white bricks.

De

At the factory, it is crushed or ground as required, water is mixed in, and the clay is extruded by means of an auger into a very long rectangular cross section that is cut into brick as it moves along the conveyer belt.

Now days, everything is automatic in most plants including the loading and unloading of bricks into and out of the kiln. (See Ceramics: Industrial Processing & Testing, John T. Jones & M. F. Berard, Iowa State University Press)

In other words, brick manufactures have a one component composition (the clay or shale). Now there is always an exception. Clays and shales happen to have some sulfate content. This is not good. You might get blistering or scumming or some other unpleasant defect.

What do they do?

They add barium carbonate or some other chemical to tie up the sulfates because barium forms insoluble sulfates. These materials are not premixed into the clay. They are just sprinkled on the clay and the extruder does sufficient mixing.

I’ll tell you a secret. Some other manufacturers may add barium sulfate such as the sanitary ware manufacturers that manufacture your bathroom fixtures. Some potters add it too.

Vanadium compounds cause scumming in otherwise pretty white bricks.

D

Now days, everything is automatic in most plants including the loading and unloading of bricks into and out of the kiln. (See Ceramics: Industrial Processing & Testing, John T. Jones & M. F. Berard, Iowa State University Press)

In other words, brick manufactures have a one component composition (the clay or shale). Now there is always an exception. Clays and shales happen to have some sulfate content. This is not good. You might get blistering or scumming or some other unpleasant defect.

What do they do?

They add barium carbonate or some other chemical to tie up the sulfates because barium forms insoluble sulfates. These materials are not premixed into the clay. They are just sprinkled on the clay and the extruder does sufficient mixing.

I’ll tell you a secret. Some other manufacturers may add barium sulfate such as the sanitary ware manufacturers that manufacture your bathroom fixtures. Some potters add it too.

Vanadium compounds cause scumming in otherwise pretty white bricks.

D

What do they do?

They add barium carbonate or some other chemical to tie up the sulfates because barium forms insoluble sulfates. These materials are not premixed into the clay. They are just sprinkled on the clay and the extruder does sufficient mixing.

I’ll tell you a secret. Some other manufacturers may add barium sulfate such as the sanitary ware manufacturers that manufacture your bathroom fixtures. Some potters add it too.

Vanadium compounds cause scumming in otherwise pretty white bricks.

D

I’ll tell you a secret. Some other manufacturers may add barium sulfate such as the sanitary ware manufacturers that manufacture your bathroom fixtures. Some potters add it too.

Vanadium compounds cause scumming in otherwise pretty white bricks.

Defects caused by raw materials are usually related to impurities or particle size. The defect can turn up at any time in the process. Here are some examples of defects caused by impurities:

Impurity Defects

Lignite

Lignite is common in many clays. It can be hard anthracite or softer bituminous coal or lignite which is softer than the first two.

Screening can reduce lignite from slurries.

Soda ash can react with soft lignite and turn it into a useful colloid that will keep the slurry dispersed.

In other words, some lignite can be beneficial in slip casting operations and other operations that use slurry. But the hard anthracite and other coal varieties are not good. They can cause blisters and pits during bisk and glost firing operations.

Clay companies have some control over the size and amount of lignite in their clays (often by blending.

You can run a screen analysis on the material and see how much lignite remains on the screens. If it is higher than the previous shipments, call the clay company and say these words: “What’s with all this lignite!”

That should get their attention. Once I said, "What is all this plastic?" (The filter bags had melted in the air floatation equipment.)

Make sure you blame them for all defects generated for the next six months. (Hey, you think I’m kidding! Make that the next two months or whenever that batch of clay is used up.)