Xerography
Definition
Dry electrophotographic process invented by Chester Carlson (1938). Photoconductive drum is charged, exposed to image, dusted with toner, transferred to paper and heat-fused. Basis of photocopiers and laser printers.
- Inventor
- Chester Carlson
- Invented
- 1938
- Core process
- Charge, expose, toner, transfer, heat-fuse
- Key component
- Photoconductive drum
- Modern application
- Photocopiers and laser printers
Common questions
How does xerography help identify a specific machine in a document case?+
Because the photoconductive drum, toner batch, and transport path leave individually distinctive marks and toner particle characteristics on a printed page, examiners can sometimes link a questioned document to a specific make, model, or an individual machine by comparing these artefacts.
What is the difference between xerography and true photographic reproduction?+
Xerography forms an image electrostatically using charge, light exposure and dry toner powder fused with heat, producing a raised toner layer that can be felt and can crack when the page is flexed, while a photographic reproduction forms the image chemically in an emulsion layer.
Related terms
- ESDA
- Electrostatic Detection Apparatus; detects latent indentations in paper by charging the surface and cascading toner particles, revealing tracing stylus pressure and writing...
- Inkjet Printing
- Non-impact printing that sprays liquid ink droplets onto paper. Two main technologies: thermal (HP, Canon, bubble-jet) and piezoelectric (Epson).
- IR Luminescence
- Emission of near-infrared radiation by ink dye molecules when excited by visible light; different ink formulations luminesce at different intensities, allowing differentiation...
- MIC / Yellow Tracking Dots
- Machine Identification Code: faint yellow micro-dots printed by many colour laser printers and copiers on every page, encoding serial number and timestamp....
- Oblique-Light Photography
- Photography of a document surface using illumination at a low angle (10 to 15 degrees from the paper plane), which casts shadows...
- Photographic Reproduction
- Lab-side imaging of a questioned document using controlled lighting (oblique, transmitted, coaxial), filters and wavelengths from UV through visible to IR, to...
- Transmitted-Light Photography
- Light passed through the paper from behind to reveal watermarks, paper-fibre disturbance, security threads, erasures and chemical thinning.
- VSC-8000
- Video Spectral Comparator by Foster + Freeman, the standard QD instrument in CFSL and GEQD labs, with broadband visible, UV (254, 365...