Anonymous ID: 5a2d9a Dec. 5, 2019, 2:29 p.m. No.7434820   🗄️.is đź”—kun

>>7434790

Same watch with the same hands. The IWC Portugese hands are heat-treated to get their blue colour. The blue comes from a very fine layer of oxidization on the metal. Because the hands are black underneath the thin layer of bluing, in certain lighting conditions, the hands may appear black.

 

"Bluing is also used for providing coloring for steel parts of fine clocks and other fine metalwork. This is often achieved without chemicals by simply heating the steel until a blue oxide film appears. The blue appearance of the oxide film is also used as an indication of temperature when tempering carbon steel after hardening, indicating a state of temper suitable for springs."

 

https://en.wikipedia.org/wiki/Bluing_(steel)