The coating is a black enamel.
By Jennifer Lynch on June 4, 2016
Feels like a powder coating. But the description says "Black Enamel Coated Metal".
By Danielle on June 3, 2016
The description provided by the seller says this: Black Enamel Coated Metal among other descriptive things:
Black Color Heavy-duty Steel S-hooks
Work great for Plants, Towels, Gardening Tools and many other use.… see more By Ila in Maine on June 3, 2016
I'm not exactly sure what the substance is but it has remained intact with considerable vibrations. I use them to hang my collection of Starbuck's mugs--about 50 of them. When the washer is on spin it makes the rod they're hanging on jump up and down but the black hasn't chipped or rubbed off. Hope this helps.
By Michelle L Carter on June 3, 2016
I think it's just a really good black paint. I have had no problems with them chipping or scratching.. I really love mine.
By Pam C on June 3, 2016