Grease pencils, also known as wax pencils and china markers, are crayon-like pencils made of wax and designed to write on non-porous surfaces. They are frequently used to mark glass, stone, plastics, analog audio tape, ceramics, photographic contact sheets and other glossy surfaces. Grease pencils are comprised of elongated pieces of wax either wrapped in paper or wood. Because the wax is soft, they must be sharpened frequently when writing on hard or rough surfaces.
Look at the pencil. Determine if it is wrapped in paper or wood. Grease pencils wrapped in paper have a string near the wax point that can be pulled to quickly and easily sharpen the pencil. If it is paper-wrapped, simply pull this string and unwrap more wax.
Hold a knife at a 45-degree angle close to the end of a wood-wrapped wax pencil.
Bare down and push the knife toward the wax tip. Shave off a small amount of wood at a time until enough wax is exposed.
Repeat this shaving all the way around the wax to fully sharpen the pencil.