Clay can sometimes undergo color changes during the firing process, and one of the common occurrences is the transformation of clay into a greenish hue. This change is primarily attributed to the presence of iron compounds in the clay and the reactions that take place during firing.
Iron is a naturally occurring element in clay and can exist in different oxidation states, including ferrous (Fe2+) and ferric (Fe3+) forms. During firing, the iron compounds in the clay can undergo oxidation, where they combine with oxygen from the air or from the kiln atmosphere.
Reduction and Oxygen Starvation
If the firing process occurs in a reducing atmosphere (with limited oxygen), iron compounds may not fully oxidize. This can result in iron being present in the fired clay as ferrous oxide, which imparts a green coloration.
Glaze and Firing Conditions
The type of glaze used and the firing temperature can also influence the color of the clay. Some glazes contain materials that interact with iron, intensifying or altering the green hue. Additionally, firing at specific temperatures can enhance the green coloration.
Artistic and Aesthetic Choice
While unintended color changes can sometimes occur, artists and potters may intentionally use the green coloration as a design element. The green tones can add depth, character, and a unique aesthetic to the finished piece.
Understanding the science behind color changes in clay can empower artists to make informed choices and embrace the natural variations that contribute to the beauty and complexity of ceramics.