Hello, You can find about this exhibit in Exploratorium's Cookbook I, page 43-1. It is called Horse's Tail. It is said in the construction instructions that a graduated material called Letraset(TM) Pantone(R) Color Paper, graduated, uncoated, 404U-G, can be be used. Hope this helps. Ali Parsa Director Zirakzadeh Science Foundation Tehran, Iran email: [log in to unmask] Tel: +98 21 878-9270 Fax: +98 21 646-2613