The corrosion would obviously have some structure. The easiest way to achieve this is by plugging the relief option into the second Picturemapwhich we have included using the mixer.Set the value to 0,1 as not to overdo it
To be flexible tho , we will load some more resources.

In the texture editor rightclick the mouse and follow the options to new/mathematical/mixer
this will load a second mixer.

In the texture editor rightclick the mouse and follow the options to new/2d textures/picturemap
This will load a third picture map.Choose bump1.jpg (Location Poser/runtime/textures/3ddj/3ddjsamplepics/bumps

In the texture editor rightclick the mouse and follow the options to new/3d-textures/noise
this will load noise (uhh obvious).

In the texture editor rightclick the mouse and follow the options to new/2d textures/picturemap
This will load a fourth picture map.Choose size3.jpg (Location Poser/runtime/textures/3ddj/3ddjsamplepics/bumps

Those are preloaded when you load SMetal4 in your library.It should look like this


Unregular Ball

Unplug the first mixer(1) from the diffuse color.
Plug the spherical map(2) into the diffuse color
Set the relief value to 1
Saved as SMetal5
Rough Ball

Plug the relief into the noise(8)
Set the relief value to 0.005
Saved as SMetal6
Rough golden Ball

Just change the diffuse color to a yellowish golden tone
Saved as SMetal7
Patternd golden Ball

Plug the first Mixer (1) to the diffuse color.
Plug the third picture map (7) into input 2 of the first mixer (1)
Plug the relief into the second mixer (6) and feed its both inputs with noise(8) and the third picture map(7)
Saved as SMetal8
Variable reflectivity

Resize the second Picture map(4) to the value 2 on both u and v and plug it to the diffuse color
Repeat this for the third Picture map (7)and plug it into the relief and also
inro the Reflection Value.
The result is a material that will reflect on the uncorroded texture parts only.
Saved as SMetal10
Variable size

Change the u and v size of the fourth picture map(9) to a value of 0.25
Then plug it into the u and v size values of the second (4)and the third picture map(7)
The result will be that the mapingsize of the texture will change depending on the contrast of the fourth picture map (9)
Saved as SMetal11
Extrude it

Just plug the fourth picture map into the displacement option.
Depending on the black and white values the surface will be more or less extruded
Saved as SMetal12