Making, polishing, and bluing screws - video

Making, polishing, and bluing screws. By Clickspring. 1:47 video:

https://www.youtube.com/watch?v=lqfIwjUNIJM


Previously:

https://www.homemadetools.net/forum/...764#post183062
https://www.homemadetools.net/forum/...593#post182268
https://www.homemadetools.net/forum/...453#post181839
https://www.homemadetools.net/forum/...8594#post87797

I don't understand the bluing technique here. In the end it looks anodized. Whatever the technique, who would have considered that a screw could look so gorgeous?