Bluing is just a coating to protect metal surfacecs. It's been around for hundreds of years as well as other metal coatings. Only in recent years have we seen powder coats or as you say, paint. I think you will see more of these in the future, as they improve. You may recall seeing chromed finishes until they ran into enviromental issues, in the USA. ...
Personally, there is nothing more beautiful than a deep, high polished blue. ..
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