I haven\'t tried doing black NMM, but I think I know what you should do. With NMM you are basically painting a 2D technique on a 3D model. Transitions between light and dark must be made quickly.
Get your black and paint it as a basecoat, then choose a spot on the model where you would normally highlight. This is where the light would hit. Work from black to pure white in that area, being careful to blend the shades together to get a smooth transition.
I\'m sorry I have no pictures to help describe what I am trying to describe but I hope you can understand it!
SENMM can either look very good or very fake in my experience. I am not too certain, but I think the \'horizon\' mark is vertical on cylindrical shapes such as space marine greaves.
Hope this was some help! Happy painting!
