Bump Normal element in additive blend materials

[jksim]

Not sure if this is the way it should work, but If I use a blend material in Additive mode the Bump Normals element is affected as well (the bump normal value for each layer in the shader is added together) - it stands to reason, I guess, but if I want to then use the Bump Normals in Nuke for relighting or any other purpose, I'm guessing it will be unusable?
thanks
Josh

[Svetlozar Draganov]

Yes BumpNormal render element will become unusable but please note that Additive Blending mode doesn't obey the law of physics and the whole material would not be physically accurate.
However there is an easy way to workaround this issue by using VrayBumpMtl available in Vray 3.0 - you could place VrayBlendMtl (without any bump maps in all sub-materials) in BaseMtl of VrayBumpMtl and you could use Composite or VrayCompTex into Bump-Map of VrayBumpMtl in order to blend multiple bump maps. This material will generate correct VrayNormal render element and at the same time it will mix materials in additive mode.

[jksim]

Nice one - pretty much as I suspected, but thanks for the tip.
Josh