Pigment Ink
Definition
Insoluble colourant (carbon black, titanium dioxide, organic pigments) suspended in a binder. Pigment particles do not migrate on TLC, so Raman, FTIR and LDI-MS dominate the comparison.
- Composition
- Insoluble colourant suspended in a binder
- Examples
- Carbon black, titanium dioxide, organic pigments
- TLC behaviour
- Particles do not migrate
- Preferred analysis
- Raman, FTIR, LDI-MS
Common questions
Why does pigment ink resist thin-layer chromatography analysis when dye-based ink does not?+
TLC separates components by how they dissolve and migrate through a solvent on a plate, which works for dyes that are soluble. Pigment particles are insoluble and simply stay put or clump, so they do not separate the way a dissolved dye does, making TLC largely uninformative for pigment-based ink.
Why are Raman, FTIR and LDI-MS well suited to pigment ink analysis instead?+
These techniques identify chemical composition directly, by molecular vibration signatures or mass, without requiring the material to dissolve or migrate. That makes them effective at characterising insoluble pigment particles in place, which is exactly the property that defeats solubility-based methods like TLC.
Related terms
- Aginsky Method
- Solvent-extraction ink-age dating (Valery Aginsky, 1996). Compares fast and slow solvent extractions of phenoxyethanol to derive an aging parameter for ink under...
- ASTM E2789-11
- ASTM standard guide for forensic examination of inks (ink-age dating context). Pairs with ASTM E1422 for paper examination by FTIR.
- Ballpoint Ink
- An oil-based, high-viscosity ink using a resin binder (alkyd or polyamide) in a high-boiling solvent (phenoxyethanol or benzyl alcohol), with triphenylmethane dyes...
- Brunelle R-Ratio Method
- Dye-degradation method (Richard Brunelle and Kenneth Pro, 1972, later refined). Tracks the ratio of extracted and unextracted dye over time to estimate...
- Dye-Based Ink
- Soluble colourant dissolved in solvent. Modern fountain-pen and dye-based ballpoint inks belong here. TLC separates the dye mixture into resolvable spots.
- Gel Pen Ink
- Water-based gel vehicle with pigment particles (often copper phthalocyanine, iron oxide). Behaves like a pigment ink on TLC but more porous on...
- Iron-Gall Ink
- A historical ink formulation of ferrous sulphate, tannic acid (from oak galls), and gum arabic. The ferrous-tannate complex oxidises to brown ferric-tannate...
- LDI-MS / MALDI-TOF
- Laser-desorption mass spectrometry. Reads dye molecular ions directly from the ink stroke with minimal sampling, increasingly used for ink-library searching.
- Optical Brightener
- Stilbene-based fluorescent whitening agent added to paper from the early 1950s onwards; under 365 nm UV the paper glows bluish white. A...
- Phenoxyethanol Decay
- Loss of phenoxyethanol solvent from a ballpoint stroke over weeks to months, measurable by GC-MS or GC-FID. The basis of the Aginsky...
- Raman Spectroscopy
- A non-destructive laser-based technique sensitive to molecular vibration modes in pigments; complements FTIR by characterising pigment molecular structure rather than bulk ink...
- TLC and HPTLC
- Thin-layer and high-performance thin-layer chromatography. Silica gel plates eluted with ethyl acetate / ethanol / water or methanol / ethanol mixes; Rf...