Question

Especially in stoneware bodies, how much percentage of fire Clay can be used -

• A. 10%
• B. 20%
• C. 30%
• D. 40%

Hint:

Logic Tip: Fire clay adds "skeleton" to stoneware. 30% provides strong structure without compromising the vitrification of the other ingredients.

Answer 1

The Correct Option is C

Concept:
Fire clay is a highly refractory (heat-resistant) secondary clay used to raise the melting point of a clay body and add structural stability (tooth) during high-temperature firings.

Step 1:
A standard stoneware body is a blend of materials: plasticizers (like ball clay), fluxes (like feldspar to encourage vitrification), and refractory structure builders (like fire clay).

Step 2:
Adding fire clay prevents the stoneware from melting, slumping, or warping at high temperatures (Cone 6 to Cone 10). It provides "stand-up" strength.

Step 3:
While recipes vary widely, a classic, well-balanced high-fire stoneware recipe often utilizes around 20% to 30% fire clay. Going above 30% to 40% can make the body too refractory (preventing proper vitrification) and overly rough. The upper standard limit for a workable throwing stoneware is typically considered 30%.

Step 4:
Given standard ceramic formulation rules for durable stoneware, 30% is a primary benchmark for maximum typical fire clay integration. \[ \boxed{\text{(3) 30\%}} \]