1. Glass Imaging Window or Platen Defects:
    • Temporary Marks: Caused by materials like fingerprints, adhesives, opaquing solutions, and debris that can produce unique but removable marks on copies.
    • Permanent Marks: Scratches or pits on the glass that persist for the life of the copier unless the glass is replaced due to obtrusiveness.
  2. Rubber-Backing Blanket Defects:
    • Can become soiled or damaged through use, potentially transferring unique features onto copies if the entire imaging area is not covered by the original document.
  3. Imaging Lens Defects:
    • Rare occurrences where dust or other matter adheres to the lens, resulting in characteristic marks on copies.
    • These defects are often noticeable enough to prompt a service call.
  4. Imaging Drum Defects:
    • Pits, scratches, or marks on the drum will produce characteristic marks and dots on copies.
    • These defects will not appear in the same place on each copy due to the drum’s rotation and may vary along the axis of feed.
  5. Paper-Feed Grippers and Rollers Defects:
    • Can leave distinctive impressions on copies, especially if the paper is not seated properly or the tension is incorrect.
    • These are typically indented impressions rather than visible toner marks and may require oblique light or an electrostatic detection device to observe.

Reference: Scientific Examination of Questioned Documents by Jan Seaman Kelly and Brian S. Lindblom

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