Hi, I have several Lodge 5-6" cast iron skillets, and after cooking about a dozen times in them (after they appeared well seasoned), a spot about 3" diameter in the center of each (inside the pan) appears to have lost some of its seasoning -- i.e., it looks grayish and unshiny as compared with the black shininess of the rest of the pan. Also, looking underneath the pan, the bottom (the part touching my gas stove burner) is likewise less seasoned although the pans had started out uniformly seasoned before I started cooking on them.
Does anyone know what might be causing this and what I can do to prevent? These skillets are small and fully fit on my burner, so it doesn't seem as though the 'worn' spots are due to the flame itself - although the flame likely is hotter in the middle (?) so maybe this has something to do with it?
Also, on a possibly related note, should we be applying oil to the exterior bottom of the pan when we apply it to the interior - i.e., after cooking before storage? I haven't been doing that and am realizing that the flame from my gas stove might be wearing down the seasoning on the exterior bottom of the pan.
And when we do stovetop seasoning, should we oil the exterior bottom of the pan to ensure the outside is properly seasoned, or is this a fire hazard?
Thank you so much as always for your help!