L11: FORENSIC EXAMINATION OF ALTERED DOCUMENTS
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what’s ESDA stand for
Electrostatic Detection Apparatus
when was ESDA invented?
1970’s
what does ESDA do?
shows impressions on documents.
what type of sheet is used in ESDA?
mylar sheet
what can ESDA also detect?
finger prints
what does the success of ESDA also depend on?
humidity time after applying toner
How is ESDA carried out?
• humid environment • document upwards, suction • mylar sheet on top • mylar exposed to ionised air • mylar selectively charged where indentations • wait • scatter black toner powder • impression is black • protect clear adhesive
what’s our visible range ?
400-700nm
what the IR spectrum range?
700-1000nm
What does IR absorption allow us to detect?
distinguish chemically different inks use to their absorbance range
IR absorption can reveal _____ _____
obliterated writing
what is tungsten light?
visible + near-IR
what colour will IR absorption images appear ?
black, grey or even vanish
what’s a soft UV light?
365 nm
what’s a medium range for UV?
313 nm
what’s a high range for UV?
254 nm
what can UV light do?
• Identify security marks • characterise products according to flurescene arising from their chemical nature • Detect emitted radiation
when is IR luminescence useful?
distinguishing between inks, which re similar in other aspects
what does IR luminescence image look like?
bright against darker backgroudn
what is IR luminescence?
Fluorescence in the IR region
How to cary out IR luminescence?
• illuminate with narrow band of visible light using a band pass filter • image with high passs filter set above band pass illumination