I have two teapots (one porcelain and the other cast iron) that

Clean them.

There might be some rust in your water.

Try cleaning the inside of the porcelain one with limeaway or something similar. Alternatively, stop being a faggot and just use a pot.

Muriatic acid.

>>941547
The brown deposit is normal wear for a tea pot. In fact it is considered a mark of tradition and sometimes even thought beneficial to flavor (I don't taste any difference). It is not a hygiene issue and is merely visually displeasing. It is hard to scrub off, use vinegar detergent. It will not dissolve by itself.

The cast iron one sounds rusted. If the liquid inside is discolored by it then it isn't tea residue but something else. Could be iron oxide, could be charring if something ever burned inside the pot. Clean thoroughly and always store dry. Consider an aluminium kettle for outdoors and an electric kettle for the kitchen. Both are cheapass products that will last a life time.

>>941547
cast iron tea pot?

how is this a thing? wont it rust like a motherfucker?

are you sure it is not stainless steel?

>>941742
It's an item from the age before cheap steel.
It requires more care than a steel kettle.
With proper care it will not rust.