I am working on a project building speaker enclosures using hollow carbon steel spheres like the kind listed here:

enter image description here

I am looking to produce these enclosures with a variety of looks / finishes, but with a consistent form factor and fabrication process, so I want to use the same sphere component as a starting point.

For one of the looks / finishes, I was thinking a blackened cast / raw iron look would be really cool, something like in these reference images:

Is there any treatment I could do to the outside of the steel sphere that would achieve this kind of look + texture?

1 Answer 1


Obscure alchemical recipes aside, the easiest way to "turn" steel into cast iron is by painting it.

The steel probably needs to be degreased (using thinner) and primed (with a metal primer). After that you can simply apply acrylic paint to the sphere.

You can mix in dirt or sand with the acrylics to get that textured look.

I would also suggest finding real-life reference for the look you're going for: your reference images look off and somewhat fake, especially too blue. Using real-life reference you could easily see the size of the particles you can mix in with the paint, and even get the sheen and reflectivity right, if so you prefer.

  • 1
    There are also tutorials available that use a mixture of stone effect spray paint (for texture), bronze spray paint (for color) sanding (more texture) and matte varnish. Or another tutorial that uses chalkboard paint mixed with sand (pretty much what you suggest in your answer, but it creates a different look).
    – Elmy
    Commented May 31, 2023 at 5:48

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