As an addendum I think the “seasoning” was some kind of matt black enamel layer on the inside of the pan. I wouldn’t have touched it but even in regular use flakes detached and I had about 6 divots in the pan because of it. Oven cleaner did nothing to remove this layer so I used by angle grinder and a sanding attachment. It was painfully slow (my grinder is cordless and needs recharging) but I cleaned it eventually. Once I was down to bare metal I cleaned it and seasoned it with a few layers of oil. I think it will be far easier to clean from now on. The outside of the pan and bottom are still coated in whatever the inside was when I bought it.
As an addendum I think the “seasoning” was some kind of matt black enamel layer on the inside of the pan. I wouldn’t have touched it but even in regular use flakes detached and I had about 6 divots in the pan because of it. Oven cleaner did nothing to remove this layer so I used by angle grinder and a sanding attachment. It was painfully slow (my grinder is cordless and needs recharging) but I cleaned it eventually. Once I was down to bare metal I cleaned it and seasoned it with a few layers of oil. I think it will be far easier to clean from now on. The outside of the pan and bottom are still coated in whatever the inside was when I bought it.