May I share what The Pan Man suggests, and I have used many times? He's a noted Griswold collector.
Get Easy Off oven cleaner with lye, you may need to go to the hardware store. With rubber gloves and goggles, and working outside, slather that pan up on all surfaces with the cleaner. Stick it in a garbage bag and seal it up tight. let it set for 3-4 days. Now with soap, water, and a brass brush used on whitewall tires, scrub it clean, gloves and goggles again. It should be beautiful gray iron. Wipe it dry right away or it'll flash rust. Now put it in a pre heated 250 degree oven for 30 minutes, to get it totally dry. Now wipe it down with Crisco, all over, and place it right side up in the oven. After 30 minutes wipe out the excess and put it back in the oven for 30 more minutes. Shut off the oven and let it cool down, and you're ready to cook.
I used this method on a 1930's Griswold that looked like it had been in a swamp since 1940, worked great.
And shame on you for having a great skillet like a 12 inch Lodge and not using it....