Why does glaze turn yellow?

Glazing is a common technique used in pottery and ceramics to create a smooth, decorative, and protective surface on clay objects. However, one issue that ceramic artists often encounter is the phenomenon of glaze turning yellow. This discoloration can be frustrating, but understanding the underlying causes can help prevent and mitigate the problem.

Causes of Yellowing Glaze:

Yellowing of glaze can be attributed to various factors:

  • Temperature Variation: Glaze firing temperatures that are too high or too low can lead to discoloration. Over-firing can cause chemical reactions that result in a yellow hue.
  • Chemical Reactions: Interaction between glaze components and clay minerals during firing can create yellowing. For instance, the presence of iron oxide in clay can react with certain glaze ingredients.
  • Impurities: Contaminants in raw materials or improper cleaning of the pieces before glazing can introduce impurities that contribute to yellowing.
  • Oxidation: Oxygen levels in the kiln can impact glaze color. Incomplete oxidation during firing can cause yellow discoloration.

Prevention and Remedies:

To maintain the desired appearance of glazed ceramics, artists can take several precautions:

  • Ensure accurate kiln temperature control to prevent over-firing.
  • Use high-quality glaze materials to minimize impurities.
  • Experiment with different glaze recipes and firing conditions to achieve the desired color.
  • Consider testing small batches before applying glaze to larger pieces.
  • Properly clean and prepare pieces before glazing to prevent contamination.

Understanding the factors that contribute to glaze yellowing and taking proactive measures can help ceramic artists create beautiful and durable pieces that stand the test of time.

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