As time goes by, the more I think of the faded or "sage" black kettles, I've got to think that it's from a combination of high heat from inside the kettle, oxidation, and possibly from being uncovered for years. My red 1960s kettle has grey porcelain inside, yet my 1978 brown and 1979 red 22's have black porcelain on the inside....my 1995 red 22 is slightly greyer inside than my '70s kettles, but not as grey as my 60s 18.5. I really think that its a combination of factors with the outside of the black kettles. Having said all that, I like the grey fades, it gives them character. I've seen anywhere from '70s to early '00s kettles in various stages of fading....my neighbor across the street has a 2000 OTS that has never been covered and it's greying a tiny bit.