It involves removing several "plugs" of ink and paper from the document, placing them in a small vial where a solvent is added to dissolve the ink.Once extracted, the ink is spotted on a high performance plate.Differentiating inks can be important in cases where a document is suspected of having been altered.A classic example is where a zero is added to a cheque making the value ten times as much.The solvent soon migrates up the plate carrying the ink with it.
Care must be taken when inks are deemed to be indistinguishable using any testing method.
Relative age comparison tests performed on inks of the same formula and written on the same type of paper with the same storage conditions (performed by measuring changing solubility properties of inks) can estimate how long inks have been written on paper.
This is done by: (1) comparing the rates and extents of extraction of questioned and known dated inks in organic solvents by thin-layer chromatography (TLC) densitometry; (2) comparing changes in dye concentrations by TLC and TLC densitometry; and (3) comparing the volatile ink components by gas chro-matography-mass spectrometry (GC-MS).
The band patterns corresponding to ink removed from three different areas of a document (Figure 1) show that samples #1 and #3 have a similar formulation while ink #2 contains different components than the other two.
This supports the Plaintiff's claim that the document was altered sometime after he signed it.