Reddit reviews The Book of Wagner & Griswold: Martin, Lodge, Vollrath, Excelsior (A Schiffer Book for Collectors)

I think there's a logo under the crud on the top.

My guesses, in this order:

1. NATIONAL small letters (Wagner) 1914-1920s No.9
   
2. NATIONAL center arc (Wagner) 1914-1920s No. 9
   
3. NATIONAL upper arc (Wagner) 1914-1920s No. 9
   
4. NATIONAL with star (Wagner) 1914-1920s No. 9
   
5. Wagner with Star 1910-1930s No. 9
   
6. "Sidney" arc 1905-1910 No. 9
   
7. Wagner High Stylized Logo with Size No. 1925-1930
   
   I'm pretty sure this is a Wagner/Sidney/National pan. Clean it, I think you will find the answer at the top. Overall construction, handle shape, hole shape...speaks Wagner to me.
   
   Reference Pages 10 - 16 of the Red Book.

Castironcollector.com is the site most people link to and their data is mostly accurate but not 100%

The Red and Blue books have even more information and serious collectors probably have both of them.

https://www.amazon.com/Book-Griswold-Wagner-Favorite-Sidney/dp/0764337297

https://www.amazon.com/Book-Wagner-Griswold-Excelsior-Collectors/dp/0764311913

I really like the old Lodge skillets. They are lightweight and very smooth. I've got a book that helps to identify Wagner, Griswold, Lodge, and other brand cast iron cookware. This web page also has useful information for identifying unmarked Lodge and other brands.

https://www.amazon.com/Book-Wagner-Griswold-Excelsior-Collectors/dp/0764311913

This one and the blue book have been awesome resources in identifying cast iron.

red book

blue book

yellow book (griswold gem pans)

grey book (early gate marked stuff)

these are about the best we have at the moment... the red book and blue book cover a lot, but obviously not everything.. and they are a bit dated as far as their pricing goes... but good sources of info.. .lots of pictures.

There is indeed "blue book"! And I mean that literally

There's also a companion "red book" which covers some of the less common brands of antique iron. Any major foundry which was making cookware prior to 1960 in the US will have something in one of those two books. If you have any specific pieces you'd like appraised, I own both books and would be more than happy to take a look, just need pics of the front and back.

The books are worth buying only if you are a collector, and even then they are only a baseline. Prices tend to move around a bit, so you usually have to check Ebay to see what things are selling at. If you are just interested in finding out a few prices, you can always ask here, or check out the books at your local library.

The two books you want are The Book of Griswold and Wagner and The Book of Wagner and Griswold. Both books cover all the major brands and have price guides.

I'm not aware of any book on cast iron restoring, but all the resources you'll need are online, such as at the Cast Iron Collector page.