A sandpaper block is a small wooden paddle with strips of sandpaper stapled to one side. You use a sandpaper block to sharpen pencils, charcoal or pastels, or to clean drawing tools.
Some pencil-drawing techniques require you to shape the pencil lead in a way that is difficult to accomplish with an ordinary pencil sharpener or penknife. Use the sandpaper block to create a pointed, flat or diagonal tip, after first sharpening a pencil with a knife or sharpener.
falmenco dancer drawing image by PinkShot from Fotolia.com
Charcoal for drawing is usually too soft to sharpen properly with a pencil sharpener or knife, and the tip of a charcoal stick wears down quickly. Use the sandpaper block to refresh the tip for fine lines or other effects.
Sharpening Pastels or Conté
Pastels, chalk and Conté crayons are generally harder than charcoal, but they are often too crumbly to sharpen easily with a knife or pencil sharpener. As with charcoal, you can refine the tip with a sandpaper block to draw fine lines.
Making Graphite or Charcoal Powder
Powdered paint image by paolanogueras from Fotolia.com
You can create interesting shading effects by applying powdered graphite, charcoal or pastel to your drawing. Create a small amount of powder using sandpaper and then pick it up with a paper stump, chamois or tissue, and draw with the powder.
To avoid making a mess when you erase lines from a drawing, use the sandpaper block to freshen your eraser. You can also use an eraser as a drawing tool, to add highlights. Use the sandpaper block to shape the eraser for the effect you want.