Lewis, looking at your full-sunlight photo, the pan looks like it may have been overheated at some point in its life. If that is true, it will not season well, and it will not turn a uniform black. Fire damaged cast iron will have a reddish, blotchy appearance. If you do not see or rub off any rust, this could be the case.
Keep in mind that a well pitted piece, especially if on the cooking surface, will be tricky to run through the electro. The pits do not give that straight line of sight from anode to cathode the set up needs to function well.