To do this, simply layer more glitter towards the tip so that more glitter is packed there, and less towards the beginning of the nail bed.I think that I could have done a better job with it to be honest, there is almost a line on the thumbnail where it is densely packed with glitter on one side and it is an abrupt change to far less dense glitter, do you see it? Sorry for the indoor picture; the sun doesn't want to come out and play!
I used OPI Here Today... Aragon Tomorrow and China Glaze Fairy Dust. It almost looks like falling snow doesn't it? Maybe next time I do a glitter gradient I will use a chunkier glitter, it would be harder to tell if I messed up!