As usual, to clean it, I boiled some water in my cast iron skillet, used a cloth and water to wipe it clean, then set it on top of the turned-off-but-still-warm burner to finish drying. When I returned to the stove, to wipe the pan down with a little oil, the seasoning lay in a powder on the surface of the pan. It had been burned off, the way you might burn off charred food remains by putting a pan or baking stone in a really hot oven. It was a preseasoned pan, and now there's a big circle of light gray cast iron showing at the bottom of the pan. I've been working on that seasoning for over a year.
I used a teaspoon of lemon juice in it for the first time yesterday, for a pan sauce, poured the sauce out immediately and washed the pan right away. I know using lots of acid isn't advisable in a relatively new pan, but it was a teaspoon in a year-old pan. Could that have ripped the seasoning off so completely? Could the burner have been too hot? Hard to believe when it was turned off and I regularly put the pan in a 500 degree oven to preheat for steaks. What happened?