Cast iron skillets stacked together.
Here's Why Cast Iron Skillets Have Rough Surfaces

Cast iron skillets have a rough texture, while others have a smooth surface. Owners of vintage cast iron skillets may wonder why pans on the market today have that bumpy texture.

The texture of modern cast iron pans can be traced back to the mid-20th century when manufacturing companies decided to skip a certain step in the pan-making process.

Vintage cast iron skillets were tumbled, removing sand from the mold and making the surface smooth. Now, that step is skipped so that sand remains, making the surface rough.

To be clear, you won't be getting sand in your food — the leftovers manifest as bumps and pits on the metal, not actual grains.