Step 1: Understanding the Concept:
Ceramic firing is a complex process where the "maturity" of the clay depends on both heat intensity and time.
Step 2: Detailed Explanation:
A pyrometric cone is a slender, pyramid-shaped device made of ceramic materials that soften and bend at specific levels of "heat work."
Heat work is the combined effect of time and temperature.
A simple thermometer (pyrometer) only measures the current air temperature. However, ceramic bodies respond to the total amount of energy absorbed.
By observing when a specific cone melts and tips over, a potter knows exactly when the chemical reactions inside the clay or glaze have reached completion.
Step 3: Final Answer:
The purpose of a pyrometric cone is to indicate the heat work during firing.