This pot was fixed up with a couple rounds of polishing.
I tried a few different substances, and one was this auto polish. They didn't indicate any ingredients, but it seemed to be a fine abrasive along with a little bit of alkaline material. It reacted with the pot and formed a gray powder, which is what happens when aluminum reacts with lye.
It turned out to be acceptable: it took off a lot of black staining and regular scratching, leaving a smooth surface that could be polished further with a finer polishing compound. It couldn't remove all the scratches, but it got most of them. Any pitting was left behind.
It's hard to say whether removing the patina was good or bad. The patina forms naturally, and is part of the pot, but it's also a bit ugly. Normal scouring also removes aluminum, and this polishing operation just removes it in a more uniform manner.
Further polishing brought out the shine, and left a reflective surface. Residual wax from the polishing should help maintain the shine a while.
Regular maintenance for this is simply to scrub with a scouring pad. It's OK for it to oxidize and develop a "dirty" surface.
Wagner Ware is a old American metal cookware brand. They were active from 1891 to 1952. Magnalite was introduced in the 1930s, and then redesigned to the current "futuristic" form shortly thereafter.
Wagner Ware was sold off, but continued the Wagner brand, and sells two lines of Magnalite products: Magnalite Classic, which is the original design, and Magnalite Professional, which is a more contemporary design.
This particular pot is from the original Wagner Ware line, and dates from between the 1930s to the 1959. In 1959, Wagner moved operations to Cincinnati and stopped using the "Sidney" designation. See: http://www.castironcollector.com/castaluminum.php and http://www.castironcollector.com/wagnertm.php
For Sale: https://www.ebay.com/itm/263894394020
Reference - about the dangers of aluminum cookware: http://www.only-cookware.com/aluminum_cookware_bad_for_health.html
