another way would be too do this.
1.Paint the spike bleached bone.
2.Paint a zig zag pattern around the base of the spike with chaos black.
3.Water some snakebit leather right down roughly 4 parts water to one part snakebite leather and wash the entire spike
4.Add the tinyest amount of black paint to the snakebite/water mix and paint away from the spike/body join along the spike ensuring to leave a little of the previous wash showing towards the tip of the spike.It is also effective to feather the end slightly
5.Continue adding teh tinyest amounts of black to the mix and highlighting in this way leaving a little of the previous colour showing and working your way back towards the body each highlight.
6.Once you've worked your way right back to the body water a little bleached bone and highlight the tip of the spike.
Couple of pics that i used this method for
Gulavhars horns
And the mumaks tusks
Hope this helps and good luck
