Galvanized steel is a material often used on larger structures like hangars, gates, houses etc. A procedural attempt is useful for avoiding additional unwrapping on background objects for instance.
My target is to create a material with a slightly grey/blue diffuse, which results from different cracks of zinc, a slightly grainy surface and some broad highlight
My main focus on that tutorial is rather on the set up of the desired material than on specific values. Result differing from mine can be rather the rule than the exception, so try out on your own. I used release 6 on this with no plug-ins, except for the lighting where I used the well known e-Light script
A few words about the geometry
Apart from the mighty mighty teapot of death and a cylinder I 'm using a beveled C-ext object on this. You can try out without beveling, but it adds a lot to the desired look and feel. My lighting setup is an e-light and an array of 9 instanced omni light with disabled diffuse lighting to kick the highlights a little bit more.
To get the color information for my basic diffuse color I open the reference picture in PS, drag a selection of my choice with the marquee tool and blur it until there are no more detail visible. Using the eyedropper tool gives me the RGB values which I use for the diffuse of a standard material.
This won't be final, it's just a base to start with, I will explain how to improve later on.
For my highlights I use a Glossiness near or equal to zero and a Specular Level around 50.
The grainy surface
For the Bump Map I choose a Noise map, set to fractal. With lowering/increasing the High/Low Threshold to values around 0,5 I increase the contrast of the Noise colors. The size depends strongly on the size of the object, a good rule by thumb is that you should rather kinda 'smell' the Bump map than see it, this requires a little trial and error.
This Bump Map breaks up the clean surface, clearly visible on the edges of the highlights.
At this point the material should be good enough for a quick and dirty aluminum or zinc material, but I' far away from the final version, so let's get it on.