Guan Style Brown Glaze Teapot Pottery

I been trying to fiqure out this teapot. I received it from a closed crate auction from China. The family had politicial involvement. The crate had other ceramics, books, etc. I know it's is from Asia, possible Guan, 19th century. I also wanted to know what you would call the glaze, and egg shell rim. I spent 6-8 hours researching. It's overwhelming. Thank you cheers