CCE Selection & Application of Materials & Equipment for Ceramics 5 — Questions and Answers
Question 1: What is the main reason nepheline syenite is preferred over potassium feldspar as a flux in some studio glaze recipes?
- It produces a brighter white color
- It melts at a lower temperature, making it suitable for mid-range firing (Correct answer)
- It has a higher silica content
- It eliminates the need for alumina
Correct answer: It melts at a lower temperature, making it suitable for mid-range firing
Nepheline syenite has a lower melting point than potassium feldspar and provides effective fluxing action at mid-fire (cone 5-6) temperatures.
Question 2: When applying wax resist to a ceramic piece before glazing, what is the primary function of the wax?
- To add color to the clay surface
- To repel glaze from specific areas, creating unglazed or design patterns (Correct answer)
- To strengthen the clay body before firing
- To fill pores in the bisqueware
Correct answer: To repel glaze from specific areas, creating unglazed or design patterns
Wax resist repels water-based glaze, leaving those areas bare or maintaining an underlying glaze layer, allowing the ceramist to create defined design areas.
Question 3: Which raw material is the primary source of alumina (Al₂O₃) in most ceramic glaze recipes?
- Silica (flint)
- Feldspar and kaolin (Correct answer)
- Whiting
- Talc
Correct answer: Feldspar and kaolin
Feldspar and kaolin are the dominant alumina sources in glaze recipes; alumina from these materials increases viscosity, durability, and firing range.
Question 4: What is the significance of the 'quartz inversion' at approximately 573°C during a ceramic firing cycle?
- Glaze begins to melt at this temperature
- Quartz crystals undergo a sudden volume change that can crack ware if heated or cooled too quickly (Correct answer)
- Clay becomes vitrified at this point
- Carbon burnout is completed at this temperature
Correct answer: Quartz crystals undergo a sudden volume change that can crack ware if heated or cooled too quickly
At 573°C, alpha-quartz converts to beta-quartz with an abrupt 2% volume expansion; rapid temperature change through this point causes thermal shock and cracking.
Question 5: When formulating a clay body for a wood-firing kiln, which property is most important to optimize for fly ash glaze accumulation?
- Very fine particle size for smooth texture
- Sufficient surface texture and porosity to hold fly ash deposits (Correct answer)
- Maximum vitrification density
- Lowest possible iron content
Correct answer: Sufficient surface texture and porosity to hold fly ash deposits
Wood-fired ware benefits from a slightly open, textured surface that catches and holds fly ash deposits, which flux and form natural ash glazes during long firings.
Question 6: A ceramist applies an underglaze decoration and then a transparent overglaze. What is the correct firing sequence?
- Apply underglaze to greenware → fire to bisque → apply overglaze → fire to glaze temperature (Correct answer)
- Apply both underglazes and overglazes to greenware then single fire
- Apply overglaze first then underglaze on bisque
- Bisque fire first → apply underglaze → bisque fire again → apply overglaze → glaze fire
Correct answer: Apply underglaze to greenware → fire to bisque → apply overglaze → fire to glaze temperature
Underglaze applied to greenware is set during bisque firing, providing a stable base onto which transparent overglaze is applied before the final glaze firing.
Question 7: Which type of glaze application method is most suitable for achieving a very even, thin coat on complex sculptural forms with undercuts?
- Dipping
- Brushing
- Spraying with an airbrush or spray gun (Correct answer)
- Pouring
Correct answer: Spraying with an airbrush or spray gun
Spraying allows the ceramist to direct glaze onto recessed and undercut surfaces that dipping or pouring cannot reach evenly, giving precise control on complex forms.
CCE Selection & Application of Materials & Equipment for Ceramics 5
What is the main reason nepheline syenite is preferred over potassium feldspar as a flux in some studio glaze recipes?