Lee, first off.... Magnet test this pan... my eyes are seeing something 'strange'.
Make certain it is CI, not Aluminum (Magnet will NOT stick)...
If Aluminum, give a holler because cleaning would be VERY different.
If verify Cast Iron, then my first step would be the Lye Bath.
Note: NO GREEN SCOTCHBRITE PADS!!! <cluck,cluck......>
Depending on coatings (type of paint, clearcoat, etc), if the lye bath does not strip it, then it is time for the 'Big Guns' ! ;D
I use ZipStrip with MC (Methylchloride)....
So far, that has worked on all kinds of paints to date....
Use only in well ventilated area, preferably outdoors. May need to coat more than one time. I usually wipe off bubbled paint with paper towels before scrubbing with Soap and Water.
Cast Iron will Not absorb anything.
It is not pourous like a sponge. The surface is sealed / solid.....
I would not be surprised to see some markings/clues, once it is cleaned up!
:) :)