Probably the idea of an upsides down cat iron n pot or pan in a hard wood fire covered in coals is better than testing. A 2,500 degree F fire is going to take all the lead and metals out. Just st the ash with soap and green water, dry, heat in an oven and season
Dark red (first visible glow): 500 to 600 °C (900 to 1,100
°F) * Dull red: 600 to 800 °C (1,100 to 1,650
°F) * Bright cherry red: 800 to 1,000 °C (1,650 to 1,800
°F) * Orange: 1,000 to 1,200 °C (1,800 to 2,100
°F) * Bright yellow: 1,200 to 1,400 °C (2,100 to 2,500
°F) * White: 1,400 to 1,600 °C (2,500 to 2,900