Determining whether your cast iron pan is rusted through or has surface rust can be done through careful inspection. Here's how you can tell the difference:
Visual Inspection: Examine the entire surface of the pan for any signs of rust. Surface rust appears as small, reddish-brown spots or patches on the surface of the cast iron. It can be relatively easy to spot and usually doesn't cover the entire pan evenly. On the other hand, if the pan is rusted through, there will be visible holes or deep pitting in the metal, and the rust may extend through the entire thickness of the pan in those areas.
Texture: Surface rust is typically just a thin layer of rust that can be removed with proper cleaning and seasoning. When you run your fingers over the surface, it may feel rough or slightly bumpy due to the presence of rust. If the rust has eaten through the cast iron, there will be noticeable craters or deep uneven texture in the affected areas.
Color: Surface rust appears as reddish-brown or orange spots on the cast iron. Rusted-through areas may have a more pronounced reddish-brown hue and could even appear darker, especially if there's accumulated grime or debris in the affected spots.
Water Test: You can perform a simple water test to identify potential rust-through areas. Ensure the pan is clean and dry, then add a small amount of water to the pan, enough to cover the suspected rust spots. If the water starts leaking through the pan or if you see water pooling underneath, it may indicate that the rust has compromised the integrity of the pan.
Poke Test: Be gentle and cautious with this step. If you suspect rust-through in a particular spot, you can use a toothpick or a small, blunt object to gently poke the area. If the object easily pierces through the cast iron or if you feel any significant weakness in that spot, it may indicate that the rust has caused structural damage.
Keep in mind that surface rust can usually be treated and restored with proper cleaning and seasoning techniques. However, if you find that your cast iron pan is rusted through or severely compromised, it may not be safe to use for cooking, and it's better to replace it with a new one. Regular maintenance and seasoning can help prevent both surface rust and rust-through in your cast iron cookware.