What is Vitrification in Ceramics?

Vitrified ceramics have been fired to at least 2192°F (1200°C), and have become water tight. This allows you to put liquids in cups, bowls, etc. without them leaking.

How water tight an object is depends on the clay. The clay body may absorb some water, but not much. Because it cannot absorb very much water, bacteria cannot spread as much through the piece. For food safety, it is recommended to vitrify pieces that will be used for drinks/food.

How do I know if my ceramics are vitrified?

Low fire clay cannot vitrify because it doesn't get hot enough. Any pieces fired to cone 6 or higher should be vitrified.

How to test vitrification in finished pieces:

1. Weigh the piece

2. Bring a pot of water to a boil

3. Place piece in boiling water for 10 minutes

4. Weigh the piece again

5. Figure out the percentage difference in weight

Porcelain shouldn't absorb any water.

Stoneware can absorb 0 - 1.5%.

Earthenware can absorb 0 - 3.5%.

If the percentage is more than listed for that type of clay, it isn't vitrified.