Step 1: Understanding Grog.
Grog is a material made from crushed or ground-up fired clay that is added to wet clay to help strengthen it. It reduces shrinkage and improves the texture of the clay, making it more stable during firing.
Step 2: Analysis of options.
- (1) Grog: Correct, grog is used to strengthen clay and reduce its plasticity.
- (2) Water: Incorrect, water is used to make clay workable, not to strengthen it.
- (3) Wax: Incorrect, wax is used for decorative purposes, not to strengthen clay.
- (4) Iron: Incorrect, iron is not typically used in strengthening clay.
Step 3: Conclusion.
Thus, the correct answer is (1) Grog.