Hello fine people.
Can you help me?
I attach two renders, one of a shiny metal material (from the free Para Studios repository) - looks good.
The other, a ‘stainless steel’ (also from the free repository) looks wierd.
I have control N’d all the geometry but it hasnt made a difference.
Do you think it is my model that needs re-doing or something else…
As always, any help would be greatly appreciated.
Cheers, Matt.
You need HDR image and AO maybe
IMO, if the model renders well with one material and not another, it’s the material, not the model, that should be questioned. Compare the settings for the shiny metal and the stainless steel and see where they differ significantly. Try adjusting the stainless settings one-by-one until the effect you don’t like is minimized or eliminated. Maybe use the values (if any) from the other material in this setting.
BTW, those seem to be some extremely fine threads on the screw object, is that an accurate depiction?
Hi, thanks for the advice.
Not sure about the HDR image…the scene has ambient occlusion with 6 samples.
The model has been imported from sketchup - maybe that’s the problem. (Although they are the same model just with different materials.)
I will try both re-modelling the bolt in Blender and tweaking the material like you say chipmasque.
The screw threads are reasonably accurate - they look fine from that view I guess.
thanks again, Matt.
That material is anisotropic, so the blurry reflections are stretched along the tangent, which is based on the UV map. I’m guessing your object is not unwraped, see here for tangent info and here for reflection info. 
Or you could just disable the little tangent box in your material settings for the weird one.
Or you could just disable the little tangent box in your material settings for the weird one.
Thats only if you really just want to map it cubicly.