Normal Maps - Is There Some Sort of Formula To Get Things Looking Right..?

Brilliant, thanks for the help. Do you have any experience using Substances with the Unreal Engine? Am just wondering how the draw calls work out with things like rust, dirt and grunge. If I have a Substance with adjustable grunge type effects and a couple of different Substances in one Substance (such as rust and grunge etc) would that be several draw calls depending on whether you had the rust etc turned on?