Excellent example! That's a really excellent instructable.
Reading that page, it's interesting that the stainless steel rivets and fastener hardware are the only bits that didn't color. Quoting from the article:
> It is possible that the stainless steel might start to color if left in the oven for longer but my cursory research lead me to believe that stainless needs to get to about 800F to color. My oven certainly can't do that.
I've heard that welding stainless steel gets it too hot and removes something (the carbon?) essentially de-stainlessing it (?). I wonder how much of that would be happening at these temperatures.
Definitely not going to experiment with this on our 20-year old wedding rings, but it seems like this is very much worth keeping in mind for any potential future projects! Maybe if I ever help one of my kids make their rings for their wedding? :)
> I've heard that welding stainless steel gets it too hot and removes something (the carbon?) essentially de-stainlessing it (?).
I don't know if it's possible, but even if it is, it's not the carbon that makes the steel stainless. It's the additional chromium, nickel, or molybdenum.
Maybe when the steel melts during the welding process, those other metals get separated from the iron.
