Yes, you can put an unseasoned cast-iron pan in the oven for preheating purposes without ruining the pan's seasoning process. In fact, preheating an unseasoned cast-iron pan in the oven is a common step in the process of seasoning the pan.
Here's how you can properly preheat an unseasoned cast-iron pan in the oven:
Clean the pan: If your cast-iron pan is brand new or has never been seasoned before, make sure to wash it with warm, soapy water and a soft brush or sponge to remove any manufacturing residues or impurities. Rinse it thoroughly and dry it completely.
Apply a thin layer of oil: After cleaning and drying the pan, apply a thin layer of cooking oil or a solid fat like vegetable shortening all over the pan's surface, including the outside and handle.
Preheat the oven: Place the oiled cast-iron pan in the oven upside down to catch any excess oil drippings. Preheat the oven to a temperature between 300°F (150°C) and 400°F (200°C).
Bake the pan: Let the pan bake in the oven for about an hour. This process helps the oil to polymerize, creating a natural non-stick coating known as the seasoning. The seasoning process forms a protective layer on the cast iron, enhancing its non-stick properties and preventing rust.
Let it cool: After the hour is up, turn off the oven and let the pan cool down inside the oven. Once it's cool enough to handle, you can remove the pan.
Repeat the process: For best results, you can repeat the seasoning process a few more times, especially if the pan is new or has been stripped of its seasoning due to cleaning or misuse.
It's important to note that the seasoning process is essential for cast-iron pans to develop their non-stick properties and prevent rusting. By preheating an unseasoned cast-iron pan in the oven with a layer of oil, you are helping to initiate this seasoning process, not ruining it. Over time and with regular use, the seasoning will improve, making your cast-iron pan a valuable and versatile kitchen tool.