What are these spots of my tea pot? How can I clean them?

I got this tea pot in Tokyo back in July and these spots started to show up in September or so. I feel like they maybe have occurred to do standing water, but I’m not sure. I don’t remember the material (maybe cast iron?) that this was made of, but I remember being excited by the material as I always look for the cleanest and best for my health. Anyways, how can I clean these spots? I’ve tried soap and water, baking soda and vinegar… any other ideas? It can sometimes leech the color into the water or my tea, and that makes me sad, so I would like to remove it. Any help appreciated, thank you!