Ok, I ordered some titanium screw to test the blackening process:
https://www.ti64.com/140ksi-titanium-bolts-s/110848.htm
https://www.instructables.com/How-to-EAS...2-Methods/
https://www.ti64.com/140ksi-titanium-bolts-s/110848.htm
https://www.instructables.com/How-to-EAS...2-Methods/