question document examination Flashcards
techniques
- VSC (video spectral comparison)
- CIE LAB colour analysis
- raman spectroscopy
- TLC- thin Laye chromatography
- ESDA- electrostatic detection apparatus
pen type characteristics
- There are a wide array of different types of ink delivery system
- Fairly simple task to determine what type of pen was used in questioned and non-questioned areas microscopically
ink delivery
Ball-Point
- Rotating steel ball tip
- Paste ink composition – -‘Solvent/Oil’ based
- Characteristic striations
- ‘Gooping’ of ink – Dot deposits or striated defects
- Furrowed
Fibre Tip
- Fibrous tip with ink reservoir
- Very solid deposition
- near brush like stroke
- Less furrowing or un-furrowed
Roller Ball
- Similar to ball-point
- More fluid ink type
- Greater ink saturation
- Generally pigment based
- No striations or ‘gooping’
- Furrowed
techniques for ink comparison
Non-Destructive
- Microscopic examination of text – To determine similarity and difference
- Video Spectral Comparison
- CIE Lab* Colour analysis
Raman Spectroscopy – Potentially semi-destructive
Destructive
- TLC – Inks must be dissolved
- HPLC/CE – Inks must be dissolved
- FTIR of ink – Not all that successful!
VSC
Although black ink absorbs all (or nearly all) wavelengths of light in the visible range…
- That doesn’t mean to say that it responds in the same way to wavelengths outside of this region
- Infra-red
- Ultra-Violet
It may be that different inks respond differently to light in these regions
raman spectroscopy
-differentiate ink types
- identify ink type
Comparison to a database of inks
- Raman – Non destructive (or perhaps semi-destructive)
- Raman SERRS (Surface enhanced) – Possible localised damage
raman spectroscopy- how does it work
Uses a mono-chromatic laser or high intensity light source to ‘illuminate’ the sample
The light interacts with the samples in a variety of ways Reflection Absorption Scattering Fluorescence – Not good!
- provides insight of the composition of the sample, a different wavelength to the original light source gives info on chemical and molecular structure
Lab* colour
A method for determination of colour coordinates
Are device dependent
- May not look the same on different platforms
CIELab* is different
Device independent
Often used as the basis for colour conversion
Lab* colour analysis
Using Photoshop to convert image to Lab* Decompose to Lab* This creates 3 monochrome layers L – Lightness a – Green/Magenta b – Blue/Yellow
Differences in colour show up as differences in brightness in the a and b layers
thin layer chromatography
Separates ink into its constituent components
A small sample of ink is removed from the document using a micro-punch
- This is then dissolved in a appropriate solvent such as methanol
Preparation
-Samples are loaded onto a TLC plate
Various types – Normally Silica
Placed in a saturated solvent tank
- Solvents systems designed to give best separation/resolution
Separation
- Solvent travels up the plate by capillary action
Separation is driven by the differential solubility of components in
The mobile phase – Solvent
The stationary phase – Silica
Polar compounds tend to have a stronger interaction with the silica stationary phase
R.F values allow lab/lab comparison or qualitative analysis
TLC
Simple – Anyone can do it…
Rapid – 20 minutes
Effective – High DP
Cheap – A few pounds
- May require chemical development
- Visualisation
- May not differentiate between very similar inks
other techniques
HPLC – High performance liquid chromatography
- Similar in principle to TLC
- Uses packed column
- Excellent resolution
- Variety of detectors
- May require greater sample conc.
EDX – Energy dispersive X-ray spec.
- Elemental composition of inks
ESDA
A technique used to develop indented marks on paper
Extremely successful non-destructive technique
- Can be used to examine writing or other indents where original has been removed
- Can be used to link documents
- Can provide results from pages up to 5 sheets below original text
- sensitive
- inexpensive
ESDA process
-Vacuum switched on
- Document placed on a sample stage and a thin film is pulled over the top
- The two are intimately held together by vacuum
-Film follows the contours of the paper accurately
- An electrostatic wand is moved over the stage
- This creates a ‘static’ charge across the document
-This is left to develop for several minutes
- Glass beads carrying toner powder are then
cascaded over the stage
ESDA
- may be affected by fingerprint techniques
- may be affected by high humidity
- may be affected by type of pen used and pressure
paper examination
Information can be yielded from analysis of paper
- Colour/Reflectance
- Density – GSM
- Thickness
- Paper type
- pH
- Water marks
- Chemical composition
Optical brighteners
-Age – Variety of techniques
U.V fluorescence
- Can be used to distinguish modern papers
- Used to achieve a ‘whiter than white’ finish
Used only post 1950 – Useful in possible forgery cases - Fluoresces bright blue under long-wave UV lighting
- Different brighteners fluoresce at different wavelengths
SEM-EDS
-Scanning electron microscopy
Can be used to examine the fine surface structure of a paper
Commonly used in analysis of historical documents
-Energy dispersive spectroscopy
Can be used to examine elemental composition
radio carbon dating
Analysis of 14C ratio of paper
Extremely uncommon in traditional forensic science
Most frequently used for historical document verification
