Noob on cast iron skillets here.
I've been in love with this type of cooking for a while and just bought yesterday on amazon my first skillet.
It's not a Lodge but a Utopian Kitchen (Chinese manufacturer).
I've used it yesterday for the first time and since it's pre-seasoned I didn't do anything before usage, just a quick wash with cold water.
I've noticed that on the first heating a circle in the skillet appeared. And it's still visible today after cooking some meat yesterday.
I'm not sure if the "circle" means that the pre-seasoning is not "well-done". By looking at other questions here, a common practice is to season again the skillet.
Is it what I should do in my case? What are the parameters to evaluate if a seasoning is good or bad?