Thanks for all the comments! I used CND powders. I started with a small black bead at the free edge which I dragged up towards the cuticle. While the black was still soft I added a bead of clear powder with glitter which I again dragged upwards, but mixing some of it with the black, so there is no obvious join between the two colours, (you need to do this quickly or they don't blend well). I then added the butterfly cane and finished off the nail with a bead of clear acrylic. Then finished as normal.