Clay preparation and firing are crucial steps in sculpture. From leather-hard to bone-dry stages, controlled drying prevents warping and cracking. Bisque firing removes moisture and hardens clay, preparing it for glazing.

Glazing techniques like dipping, pouring, and brushing create diverse finishes. Glaze composition, including silica, flux, and alumina, affects the final appearance. Understanding firing temperatures and potential defects is key to successful glazing.

Clay Preparation and Firing

Stages of clay drying

• Leather-hard stage clay partially dry yet workable enables trimming and detailing
• Bone-dry stage clay completely dry ready for firing becomes fragile and breakage-prone
• Controlled drying prevents warping and cracking ensures even moisture loss throughout piece
• Humidity, temperature, and air circulation affect drying process
• Slow drying under plastic covers, damp boxes for gradual moisture loss, rotating pieces for even drying

Process of bisque firing

• Initial firing of clay before glazing typically at lower temperatures (1650-1900°F)
• Removes remaining moisture hardens clay for easier handling creates porous surface for better glaze absorption
• Loading kiln, slow temperature increase, hold at peak temperature, gradual cooling
• Chemical water removal, quartz inversion, organic material burnout occur during firing
• Prepares clay for glazing by creating ideal surface conditions

Glazing Techniques and Composition

Techniques for glazing application

• Dipping submerges entire piece provides even coverage suitable for uniform application
• Pouring glaze over piece useful for internal glazing of vessels creates unique flow patterns
• Brushing allows detailed designs and patterns suitable for layering multiple glazes
• Spraying achieves smooth even coverage ideal for large surfaces or gradients (spray gun, airbrush)
• Wax resist creates unglazed areas useful for patterns or preserving textures

Fundamentals of glaze composition

• Basic components silica (glass former), flux (lowers melting point), alumina (stabilizer), colorants (metal oxides)
• Types transparent, opaque, matte, glossy each with distinct visual properties
• Glaze-clay interactions thermal expansion compatibility, clay body absorption, chemical reactions during firing
• Firing temperatures affect glaze behavior low-fire (1740-2012°F), mid-range (2124-2264°F), high-fire (2305-2372°F)
• Glaze defects crazing, shivering, pinholes, blistering require troubleshooting
• Special effects crystalline glazes, raku firing, luster glazes create unique finishes