the gems aret quite doing it for me. you have the basic idea, but remember to go to white. a white point in the darkest region (i like to almost go to black and a THIN line along the edge of the lightest region (this can be given texture to give the imprtession of a grain, works wonderfuly for a tigers eye effect->sunburst to snakebite to black with white) also, if your doing layering, try for a smother transition by using more of them (basicaly "feathering"). i like a gloss coat on them too.