Ceramics 106: The basics on Crystalline Glaze

Introduction to Crystalline Glaze

Overview of the Video

• The video serves as a concluding installment in a series on crystalline glaze, focusing on its chemistry, application, and firing techniques.

• The presenter introduces crystalline glaze as a clear glaze that can contain color and features microcrystalline and macrocrystalline structures.

Composition of Crystalline Glaze

• The basic recipe for crystalline glaze includes zinc oxide, silica, and a chosen frit; these components are essential for crystal formation during firing.

• Emphasis is placed on the importance of the firing schedule in controlling crystal growth due to the simplicity of the glaze's composition.

Types of Crystals in Glazes

Exotic Crystal Structures

• Discussion includes business crystals and molybdenum crystals, which have unique structures compared to standard crystalline glazes.

• The presenter notes that information about these exotic crystals is scarce, making them somewhat of a trade secret within the ceramics community.

Enhancing Color in Crystalline Glaze

Additives for Color Variation

• A simple recipe can be enhanced with various colorants found commonly at home; this allows for creative experimentation with colors.

• A chart is provided showing common colorants that can be added to achieve different hues; viewers are encouraged to pause and take notes.

Experimentation with Colorants

• Suggestions include using uranium oxide for yellow coloration (noting it does not glow in the dark), along with other additives like cobalt or rutile which affect crystal growth differently.

Understanding Additives' Effects

Role of Various Additives

• Cobalt reduces crystal amounts while rutile promotes growth but should be limited to 5% by weight to avoid excessive crystallization.

• Other additives mentioned include calcium (reduces shrinking), alumina (increases viscosity), and boron (impedes large isolated crystal formation).

Preparing for Firing

Importance of Catch Bases

• A catch base is crucial when working with runny glazes; it prevents pieces from sticking to kiln shelves during firing.

Creating Your Own Firing Schedule

High Fire Crystalline Glaze Techniques

Understanding High Fire Crystalline Glazes

• High fire crystalline glazes are typically fired at cone 10, requiring temperatures around 2300°F or higher for proper melting.

• The process involves a soaking period where the temperature is manipulated to encourage crystal growth after the glaze has melted.

Crystal Formation Techniques

• Different shapes of crystals can be created during the soaking period by carefully controlling temperature rises and drops; halos, rods, axes, and false circles (flowers) can all be formed.

• Specific temperatures yield different crystal shapes: rods form at approximately 2008°F, axes at around 2012°F, and full circles (flower-like structures) between 1850°F to 1994°F.

Manipulating Crystal Growth

• Hybrid shapes can be achieved by combining techniques—manipulating how long you hold at specific temperatures and adjusting the rate of temperature changes is crucial for desired outcomes.

Factors Influencing Crystal Development

• Various factors affect crystal growth including kiln type and positioning of pieces within the kiln; even slight differences in firing schedules can lead to distinct crystal formations.

• Consistency in temperature control is essential for successful crystal production; experimentation with one's own kiln is recommended rather than strictly following external firing schedules.

Conclusion and Resources

• The speaker plans to share their own firing schedule and a glaze recipe as practical resources for viewers, emphasizing that while these are effective recipes, they may not represent their best-kept secrets.