Temperature and color of baked blue in iron pan

When the temperature reaches 500℃, the color will turn blue.

When the iron pot is heated to about 500℃ at high temperature, a chemical reaction called roasting will occur. Oxygen and water molecules in the air combine with iron atoms to form Fe3O4, which makes the whole surface appear dark blue. Blue is a visual effect due to the reflection, refraction and absorption of light on the surface of matter.