Reconditioning a pan

My sister found a #14 Large Block logo EPA in her basement that she thinks used to be my grandmothers. I almost cried when I saw the condition especially on the cooking surface which was rusty. I commenced to clean it up in my usual way in a lye bath, followed by a very short 1/2 hour 50/50 water and vinegar bath. then I tried to scrub and scrub and scrub the best I could. The pan came clean enough on the back where the logo is, but the cooking surface has black specks that are raised up and some minor pits where I managed to scrub off and wire brush the black spots. I'm sure it is due to rust damage to the metal as they are located in the area where the pan was most rusty. My question is how to remove the black spots with doing the least amount of damage. It doesn't appear that the spots will come off in the lye and I am concerned that a prolonged soak in vinegar will cause more pitting than is necessary. It may be necessary to accept the pitting as the damage might already be done, but I would like to not cause any more damage due to a mistake in improper reconditioning. I though about boiling water in the pan to see if that might do something or boiling some water with some vinegar. This isn't my first piece of cast iron but I am not a veteran either, and this piece means a little more than something at a garage sale or on ebay. Please help. I Attached photo of the spots.

I would first go at them with full strength white vinegar (use a spray bottle) and 000 or 0000 steel wool. Work on them a few minutes at a time and then rinse. Don't leave to soak more than a couple minutes first.

A product called Evaporust is also very useful in these situations. A non-toxic chelating agent, it can be safely used. Just a fraction of an inch poured in the bottom and putting plastic wrap over the top to prevent evaporation is an idea. Not inexpensive, but if you do a lot of pans, a bottle could be a good investment.

Thanks for the tips Doug, I just ordered the evapo rust to see how that will do. 9 bucks on amazon prime for 32oz. Pretty cheap to try. Do you think that setting up an E-tank would help gently remove the rusty spots. Not something I was looking to do in the near future especially the size necessary for a #14, but I will if it is the best way.

Spots like those appear to be the residual from where rust acted on the piece. It may be that we don't notice them (or as much) on as-cast surfaces vs. polish ground ones. Electro will remove active red rust and carbonized build-up, but sometimes stains like these persist.

If it was just a stain I would leave them alone and season over, they are actually bumpy above the surface of the pan, some of the smaller areas scrubbed off but the larger ones persist, and some of them have left very, mild pitting after scrubbing off. So I assume in order to have a working cooking surface I need to remove all the bumps and if there is pitting as a result then I can season and over time to fill in the pits as best as possible with cooking seasoning, I have a slant logo #9 with an 1/8 inch u shaped pit on the cooking surface and it cooks just fine with no problem sticking. I know what you mean about as-cast. My newer lodge pan looks like the bumpy surface of the damaged old one.

A spatula or a putty knife and vinegar should remove the carbon specks. The pits will fill in with seasoning which can also cover any scratches.

Hilditch

Thanks W.Hilditch. Just for s&g's I went ahead and put the pan on the stove with water and heated to a boil then used a spatula as you were describing and as if I were cleaning stuck on food out of a seasoned pan with water. It did a pretty good job of getting most of the carbon specs out even without more vinegar. Will still need some work and I am going to try the evaporust as well when it gets here.

A cheap way to remove rust is a molasses bath. I go 4:1 water:molasses.
Its sort of like a lye bath. Not fast, but it works.
If you can rub sandpaper on something and get red, its still rusty. If you have something above the metal, its still rusty. Rust removes metal.
Evaporust is a phosphoric acid product if I recall, and you can get that for less (and dilute it) in the paint section at the home store.

It's a "selective chelating agent", not an acid.

Which it would that be?

EDTA, apparently.