D'Addario Classic Celluloid Thumb Picks shell-coloured thumb picks are produced from the highest quality Celluloid. Celluloid is one of the most popular guitar pick materials today. It's available in a wide variety of shapes, colours and thicknesses, and provides a natural feel and warm, fat tone. A man-made material, Celluloid was first introduced in the early 1900s as a substitute for natural Tortoiseshell picks.