Chinese Yixing clay teapots are handcrafted items that are often seasoned over time.
The burnt aspect suggests that the clay has undergone a high-temperature firing process, which gives it a unique, durable quality and enhances its natural colors and textures, ranging from deep reds to purples and browns.
For more information about this teapot and the tea I've brewed with it most frequently, visit:
Yixing Clay Teapot & Pu-Erh Tea Wrappers - a blog post in English.
Or the Danish version here: En historie om Pu Erh-te og kærlighed, which translates into 'A Story about Love and Pu Erh Tea'.
Pentax K5 & Carl Zeiss 35mm f/2 distagon.