VSC
Definition
Video Spectral Comparator (Foster + Freeman VSC-8000 series). Workhorse QD instrument combining UV, visible and IR sources with IR-sensitive cameras for ink, paper and secret-writing examination.
- Manufacturer
- Foster + Freeman
- Product line
- VSC-8000 series
- Illumination
- UV, visible, and IR sources
- Detector
- IR-sensitive cameras
- Primary use
- Ink differentiation, paper examination, secret writing
Common questions
How does a VSC reveal indented or erased writing that the eye cannot see?+
Oblique raking light and infrared luminescence make surface indentations and altered fibers cast shadows or fluoresce differently from the surrounding paper, and IR viewing can penetrate certain inks that are opaque to visible light, exposing text hidden beneath overwriting or obliteration.
Can a VSC prove two inks are chemically identical?+
No. It differentiates inks by their optical response under different wavelengths, which is useful for showing entries were made with different pens, but confirming chemical composition or dating an ink requires separate methods such as thin-layer chromatography or mass spectrometry.
Related terms
- Charred Document
- Paper that has been burned to the carbonised stage but not fully reduced to ash; the cellulose has pyrolysed and the sheet...
- ESDA
- Electrostatic Detection Apparatus; detects latent indentations in paper by charging the surface and cascading toner particles, revealing tracing stylus pressure and writing...
- Glycerin Chamber
- Sealed humidification chamber held at 60 to 80 percent relative humidity using glycerin-water solutions to restore flexibility to charred or brittle paper...
- Indentation
- Latent pressure impression left on a lower sheet of paper when writing on an upper sheet; depth depends on pen pressure, paper...
- Oblique Light
- Side lighting at a low angle (5 to 15 degrees from the paper plane) that throws indentation shadows. The simplest indented-writing technique,...
- PVA Spray
- Polyvinyl-acetate solution sprayed in a fine mist to consolidate the surface of a charred sheet so it can be handled, mounted and...
- Secondary Writing
- Term for indented impressions: writing recovered from a sheet beneath the original, also called secondary or transferred writing.
- Steganography
- Concealing one file inside another in a way that hides the existence of the hidden file. LSB image manipulation, JPEG DCT coefficient...
- Sympathetic Ink
- Older name for invisible ink; the writing develops (becomes 'sympathetic') only after a heat, chemical or UV stimulus is applied.