question document examination

Question 1

techniques

Answer 1

• VSC (video spectral comparison)
• CIE LAB colour analysis
• raman spectroscopy
• TLC- thin Laye chromatography
• ESDA- electrostatic detection apparatus

Question 2

pen type characteristics

Answer 2

• 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

Question 3

ink delivery

Answer 3

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

Question 4

techniques for ink comparison

Answer 4

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!

Question 5

VSC

Answer 5

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

Question 6

raman spectroscopy

Answer 6

-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

Question 7

raman spectroscopy- how does it work

Answer 7

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

Question 8

Lab* colour

Answer 8

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

Question 9

Lab* colour analysis

Answer 9

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

Question 10

thin layer chromatography

Answer 10

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

Question 11

TLC

Answer 11

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

Question 12

other techniques

Answer 12

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

Question 13

ESDA

Answer 13

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

Question 14

ESDA process

Answer 14

-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

Question 15

ESDA

Answer 15

• may be affected by fingerprint techniques
• may be affected by high humidity
• may be affected by type of pen used and pressure

Question 16

paper examination

Answer 16

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

Question 17

U.V fluorescence

Answer 17

• 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

Question 18

SEM-EDS

Answer 18

-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

Question 19

radio carbon dating

Answer 19

Analysis of 14C ratio of paper
Extremely uncommon in traditional forensic science
Most frequently used for historical document verification