I can't begin to tell you how many times, when I have nearly finished a drawing, when all of sudden, no more pigment would adhere, to the surface of my paper. I have ruined drawings completely, due to this, causing the surface of the paper to tear. The reason why this occurs, is because the paper has ran out of tooth and has become to slick for pigment to adhere. So, what you need to do is, create some tooth to the surface of the paper. Here are a few tips, that I have learned from several art friends and artists, when facing this dilemma.
• Try spraying the surface of the paper with Krylon Workable Fixatif. Make sure you let the paper dry for at least 30 minutes to an hour, before you begin adding more layers of color.
• Try using a very fine sandpaper softly over the area not adhering.
• Try using a solvent to breakdown the wax, such as Turpenoid Natural.
• Try switching to a softer pencil, such as the water soluble pastel pencil Caran d'Ache Neocolor II Artists' Crayons.
• Try burnishing a piece of self-adhesive frisket film over the top of the saturated surface and then lift off some of the pencil.
• If you intend to burnish your drawing, make sure you wait til the end, as burnishing will take all the tooth out of the paper.
Keep on Creating!