Why is tea rust so important to old teapots?

I heard a story before. A collector took a fancy to an old teapot used by a rural grandmother in the country all her life, and was willing to pay a high price to buy it and make an appointment to trade it another day. Grandma is very happy to see that her pot is so old and can still fetch a good price. In order to thank the buyer, grandma worked hard to clean the teapot inside and outside, and the teapot was brand new. But at the time of the transaction, the buyer didn't want to say that it was not the pot he wanted to buy. Grandma explained it for a long time, but the buyer left sadly. The buyer said that he was interested in the obsolescence of the old pot and the tea rust on the inner wall. Without these, the teapot is worthless. Why is tea rust so important? That's because the purple teapot has been used for a long time, and there is a layer of brown-red tea rust on the inner wall. The longer it takes, the more tea rust accumulates on the inner wall, so the more mellow the tea soup is after making tea. Long-term use of purple sand teapot, even if you don't put tea leaves, just pour boiling water, still exudes attractive fragrance, which is beyond the reach of ordinary tea sets. The characteristic of teapot is that it doesn't take away the aroma of tea and has no taste of cooking soup. The wall of the teapot absorbs the fragrance of tea, and after long-term use, pouring boiling water into the empty teapot will also have the fragrance of tea. According to scientific analysis, it is because the sandy teapot will absorb tea juice and accumulate "tea rust" after being used for a period of time, so the boiling water injected into the empty teapot also has tea fragrance, which can maintain the original flavor of tea soup and has the characteristics of cold and heat resistance. The country woman didn't know the real value of her old teapot, so she made a joke and didn't say it, which is a pity.