Black natural finish for steel or iron exterior building parts

I am building a custom Arts/Crafts building and using exposed steel connectors and straps.
What are suggestions for a "natural, black" finish. Some connectors are on exterior.

Edward Van

2006

Try 20 gm tannic acid ⇦this on eBay or Amazon [affil links] /15 gm phosphoric acid/ 1 lit water(do it yourself rust converter ⇦this on eBay or Amazon [affil links] ). It must be clearcoated (Everbrite [a finishing.com supporting advertiser]). Good luck and hope it helps!

Goran Budija

2006

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