2-70. Why should you use a sky-blue pencil to mark a board before photographing  it  on  black-and-white film? 1. 2. 3. 4. Because no colored marks reproduce  on  black-and-white film Because  sky-blue  lead  fades under the intense light of the camera Because  photographic  black-and- white films are blind to sky- blue Because  sky-blue  pencil  leads are wax-based and melt under the camera lights 2-71. Why must you constantly move an electric eraser over an error in a circular  pattern  instead  of concentrating  on  it? 1. To lighten the image area around  the  error 2. To prevent damage to the paper surface 3. To keep your wrist from tiring 4. To  blend  in  the  correction 2-72. What eraser should you use to pick out highlights in a drawing? 1. A  plastic  eraser 2. A  kneaded  eraser 3. An art gum eraser 4. Pulverized  eraser  particles 2-73. What is the purpose of an erasing shield? 1. To isolate areas you want to erase 2. To shave eraser particles away from  the  drawing 3. To protect the eraser from dirt on the drawing 4. To  protect  the  drawing  surface you do not want to erase 2-74. What is the purpose of a stump or tortillon? 1. To blend pencil, charcoal, pastels,  and  crayons 2. To blend color and ink washes 3. To mix binders with pigments 4. To mix pigments 2-75. To make sure you are making a clean and accurate cut, when should you change the blade in the knife? 1. Daily  only 2. Weekly  only 3. Monthly  only 4. As often as you feel the blade needs  changing 11