Is pottery really made from dirt?

Question: Is pottery really made from dirt? Is it safe to use?

Answer: Yes, it’s true. When you set your table every night, you’re setting it with dirt.

kaolin-clay-mine

An old open-pit, kaolin-clay mine in Hitchcock Woods, Aiken, South Carolina, USA. Photo by carlfbagge (www.flickr.com).

Pottery is nothing more than soil clay that has been mined, cleaned up, dispersed, sieved into its finer particles, and settled out to be used. A nice summary of this process is found in an article by Phyllis McKee: http://www.infoplease.com/spot/clay.html.

Three general types of clay are used in making pottery. Porcelain has as its main ingredient a clay type called kaolin. In the terminology of mineralogy, kaolin is a 1:1-type clay that is not very plastic—or easily shaped—and not very sticky, so it will tear if too much stress is put on it. It is the purest material used in pottery and when fired may not need a glaze because it comes out so shiny.

The plates you eat off of are made from stoneware clay, which typically is a combination of materials that include comp kaolin, silicas, and feldspars. Then there is earthenware clay. This contains a wide variety of minerals, including things like iron oxide.

No matter what the type of pottery, dirt is your basic material. But eating and dirt aren’t just connected through the making of pottery. There is something called geophagy—a term that describes the custom of people around the world eating dirt. It appears to be a method for indigenous peoples to improve their nutrient intake. One example comes from the high plains populations of Peru, where local folks dip their baked potatoes into a slurry of soil before eating them.

–Answered by Nick Comerford, University of Florida

Have a question for Soils Matter? Post it as a comment below, or email us at soils-matter@soils.org

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s