answer:Yes, it is because they were designed to write on smooth surfaces such as glass or china. From Pencil Things Info: “This specialty pencil goes by many names – such as wax pencil, grease pencil, or china marker. It provides a good solution when you have to write or draw on a smooth surface to which most other writing tools do not adhere, such as glass, metal, polished stone, ceramics, plastic, and mylar. It is easily removed from such surfaces with a dry tissue.”