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 f

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.

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 fl

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.

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 f

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.

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 f

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 f

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.)

Grit

We had a recurring blistering problem in fine china where I once worked and for years nobody could figure out what was causing it.

I was new with the company but not inexperienced in solving material problems.

I called each of our suppliers and said that we had blisters and it was their fault.

The representative from a kaolin company asked, “What’s the grit?”

I wasn’t sure what he was talking about because I had not used that particular clay before. Rather than tell him that I didn’t know what he was talking about, I said, “Hold on a minute.”

I asked the quality control manager, “What’s the grit in that stuff?”

He had a questioning look on his face despite his 30 years of service. He pulled out the specification sheet for the last shipment, found that there was such a thing as "grit," and gave me a number.

The number represented the amount of coarse material that showed up during a screen analysis of the clay. For this particular clay, the grit was in the form of mica.

Mica is not good!

Hearing the number, the representative said, “That is too high! I’ll call the mine!”

We set a control standard and never had that problem again.

I‘d paid my first years salary in five minutes a few days after joining the company.

Iron and Manganese Compounds, Silicon Carbide, Soy Beans and Salts

Sometimes clay manufacturers ship clays to storage areas by rail, ship, or barge. Dockside raw material storage is always dangerous for contamination. The reason is that these facilities ship iron ores, ferrosilicon, silicon carbide and they are not very careful about cleaning out a shed of ferrosilicon or other contaminant before loading it with a shipload of clay. (We changed from bulk to Super Sack® shipments.)

Some of these materials give off oxygen when they decompose. That occurs at some characteristic temperature.

We used the same British china clay in two different plants.

In one plant we had blisters in our decorated ware, the worst possible condition.

The other factory using the same clay didn’t. Why? The bisk temperature was much higher in the not affected plant. The contaminant, a manganese compou