I honestly do also Valerio, and you know, I am not sure that I have ever
heard, or seen someone explain how the 'bluing' happens, or is caused !
Leave it up to the one and only You sir to enlighten us, to teach us such a
thing, or things. 📚🥇And I had always heard that it was sort of due to
a heating process that we get that cool blue, but I didn't connect it to how
exhausts can get 'blued' as well.

Oh, and although I never have had a motorcycle, I remember years ago we
had a 1990 Mustang GT which we put new headers on, and they got 'blued',
'greened', 'red', purple', maybe even 'gold' just like in the pic of that cool
motorcycle above.

Yes, no doubt Valerio, I think it is great as well, and the same goes for this
post here this Monday, so thanks a ton !!!

 

Indeed, I prefer blued screws. My Mühle Glahütte has blued screws (and gold chatons, something else I like).

I have that same colouring on the exhausts of my BMW R1100R and R1150GS.

You can also apply the same process to steel hands:

 

Muhle Glahutte, and BMW, two 'blued' beauties no doubt Hector !!
From watches, to cars, and everything in between, it;s just great to
talk with you and everyone and learn from all of you guys of course.🥇
Honestly, I don't think there is a day that goes by where I, oe all of
us either don't learn something new about watches, or life in general
to tell the truth. ⌚✨And it is just THE best, so I thank You along with
Valerio, everyone who is here for being so amazing !!!

 

Heat Bluing has also been used on some of the Italian made Colt Peacemaker clones. Not as wear resistant as chemical bluing per what I have read but typically chemical bluing is more black in color than heat bluing.