These delicate pieces are called split bowls. A thin bowl is turned and then cut in half. It is then reglued on a different axis to form another shape. On my 3 pieces i have embellished with inlays, piercing with a dremmel and other shapes that were fromed by sawing, sanding and drilling.
Original idea came from Alan Carter. Full demo here:
More of my work @ www.facebook.com/pages/Simon-Beggs-Wood-Turning/174188352624110