This isn’t perfect but should be good enough from a distance.
It mixes two separate mixtures of diffuse and glossy, mixed using the same factor but in reverse to each other.
There should be an element of anisotropy (which isn’t in this shader) but it doesn’t get applied in the real world in the same way as in brushed metal. Galvanisation uses crystallisation and the direction of the anisotropy depends on the positioning of the crystals or “cells” in a voronoi texture.
I have tried variation in shades (it’s greyscale) rather than colour. You can do that yourself with the brightness and contrast controls. If you make the variation too noticeable it doesn’t really look anything like galvanised metal then.
The cells are in the voronoi texture. They’re not all the same shape. If you change the scale in my .blend file to, say, 10 you will see that.
Hum, it doesn’t look like metal. Maybe you should work more on the “galva texture”, it’s not just a Voronoi. Add some imperfections to the surface, and maybe use the normal input. I tried, it’s not perfect but it’s not that far from reality I guess.
Thanks. I actually put it together for a very nearly diffuse metal and it looks OK from a distance for that. The problem is I don’t think you can get really close to galvanised metal with a procedural texture because the imperfections are like stretch marks but in different directions for each “cell”. That’s why the anisotropic shader makes it look fake.
I say that it looks more like a concrete shader but nice try.
Make it more shiny.
I have my own metal shader.
If you want to see it then reply this message.
It doesn’t look like concrete. It’s flat. Also, you can make it glossier than in my image above by adjusting the mix, but I was aiming for a dull galvanised coating you get from dry galvanising (“Sherardising”) the metal. Here is a glossier version.
