1. Fundamental Causes
- Thermal Stress:
• Clay (α=5.4×10⁻⁶/°C) & glaze (α=7.1×10⁻⁶/°C) coefficient mismatch
• Generated during cooling from 1300°C→200°C at ~15°C/min rate
- Crystalline Growth:
• Mullite (3Al₂O₃·2SiO₂) needles form at 1100-1250°C
• Agate particles create localized stress points
2. Formation Process
Stage 1 (Firing):
• 0-900°C: Clay body shrinks 8%, glaze remains fluid
• 900-1300°C: Glaze melts, encapsulates agate particles
Stage 2 (Cooling):
• 1300→800°C: Primary cracks form (50-200μm wide)
• 800→200°C: Secondary branching occurs (10-30μm)
Stage 3 (Aging):
• Years 1-5: Tea tannins deposit in cracks (0.01mm/year)
• Years 5+: Iron oxidation darkens veins (Fe₂O₃ migration)
3. Unique Characteristics
- Directionality:
• 75°-110° branching angles (determined by quartz content)
• Never intersects glaze bubbles (Φ<0.2mm)
- Acoustics:
• Crack density affects sound frequency (280-320Hz ideal)
• Dull "thud" indicates over-cracked inferior pieces
4. Modern Quality Standards
- A-grade:
• 3-5 main veins/cm² with dendritic branches
• Vein depth = 0.1-0.3×glaze thickness
- Reject criteria:
• Cracks reaching clay body
• Symmetrical "spiderweb" patterns (indicates artificial quenching)
5. Distinguishing Features
- Natural vs. Artificial:
• Authentic: Veins follow agate distribution (random but logical)
• Fake: Uniform depth/length (acid-etched)
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