@Teafortea
https://hojotea.com/item_e/mumyoi.htm
It is said that Mumyoi teapot becomes very shiny after using it for some time. When it is well-seasoned, you can actually see your reflection on its surface. After being heated, the red clay shrinks to more than 30%; the gaps between the clay structure is compacted and are very close together. It easily traps substances from tea and thus forming a very shiny surface.
Many customers describe that the texture of Mumyoi teapot is as smooth as silk. There is another important process which contributes to this fine texture of Mumyoi teapot. The process is called "Namamigaki". It is carried out after teapot is partially dried at room temperature. The surface of the teapot is pressed by rods or stone to smoothen and harden its surface. This process is the most time-consuming work but it makes the surface of the clay very solid and tight. Even the "Namamigaki" expert can only complete 5 teapots in a day. Each teapot requires at least two times of "Namamigaki" process.
That said, yours seem a lot shinier than most other mumyoi I've seen. Lots of extra effort in the burnishing