This technique can be applied to gems, scopes, glasses, buttons, and anything of the like. Its really not that hard you just have to understand the concept then apply it
Step 1: Apply your basecolor, most people use reds, greens, and blues but its up to you.
Step 2: Apply a lighter shade of your base coat below half way.
Step 3: Keep applying lighter shades until you reach the bottom and/or desired look.
Step 4: Add darker shades near the top just like you did with the lighter shades.
Step 5: Add one large dot and one smaller dot of pure white or pure white with a litle bit of your basecoat.
Step 6: Put a little gloss varnish over it to give it the shine if you like. Your done!
Thanks to cookster from www.40kforums.com for this.