1. The Analytical Chemistry of Ink
Ageing
Group Meeting
Monday, Dec 02, 2013

2. Ink
• Many different ink compositions
• Solvent(s)
• 2-Phenoxyethanol
• Resin(s)
• Pigment(s)

3. Paper
• Cellulose
• Treated cellulose:
• Glossy
• Made from recycled material
• Coloured
• “Hairy” or “smooth”

4. Pen stroke
• Straight line versus curved line
• Pressure applied

5. Analysis – Database scouring
• Curating a database of pen inks from various
companies and years
• Create drying curves for each ink
• Match the unknown ink to a curve(s) in the
database based on a sampling

6. Analysis – Dynamic Ink Ageing
methods
• Three methods covered
• Rate of decrease of volatile components of ink
(R threshhold value)
• Rate of decrease of solvent extractability of
ink (D threshhold value)
• Determining the ink age factor (V% threshhold
value)

7. Dynamic ink ageing methods

8. Method 1: Rate of decrease of volatile
components R%
• Hole punch sampling of ink
• One sample is dissolved (P); the other sample
is heated then dissolved (PT)
• R% = [(P-PT)/P]*100

9. Method 1: Rate of decrease of volatile
components R%
• Expect less solvent to be present after heating
• Small solvent present = small loss after heat =
Old sample
• Large solvent present = large loss after heat =
New sample
• If the difference between before and after
heating is large, then (P-PT) will be large.
• (P-PT)/P will be closer to = 1

10. Method 2: Rate of decrease of solvent
extractability (D)
• Hole punch sampling (duplicates)
• One sample duplicate is not heated. One dissolved in
weak solvent, the other in strong solvent
• The other sample duplicate is heated. One dissolved in
weak solvent, the other in strong solvent

11. Method 2: Rate of decrease of solvent
extractability D
• Expect less solvent to be present after heating
• Uses two solvents: slow-extracting weak
solvent and fast-extracting strong solvent
• Achieves the same effect as Method 1, but has
a two-solvent descriptor of phenoxyethanol
differences
• D = P – PT;
• D = 100*[(Mw,u/(Mw,u+Ms,u)) - (Mw,h/(Mw,h+Ms,h))]

12. Method 3: Determining the ink age
factor V%
• “Headspace GC-MS”: two temperatures for
desorption
• No solvents

13. Method 3: Determining the ink age
factor V%
• Statistical Neumann’s trend test
• n = # measurements (x) chronologically
ordered; s = standard deviation
• Given a probability level (Conf. Interval), what
is Q in relation to the threshhold value

14. Method Validation
• Interlaboratory validation is a huge problem
• Needed for application to real cases
• Forensic science tends to be a bit secretive
• Current ink dating methods need to be tested
randomly by other labs for their robustness
etc...

15. Interpretation of ink ageing analysis
• Likelihood ratio
• Accepting normal
distribution
• Two or more hypotheses
• d = a given value of D
• Likelihood of one hypothesis being more true
than the other

16. Conclusion
• Because there is not an extensive body of
research supporting and validating these
methods, forensic scientists need to present
their findings with humility and full awareness
of the advantages and disadvantages.
• Confine reports to within the empirically
tested bounds of the field, intelligently
understood (not relying on a single study or
conference proceedings)