Dye-Based Ink
Definition
Soluble colourant dissolved in solvent. Modern fountain-pen and dye-based ballpoint inks belong here. TLC separates the dye mixture into resolvable spots.
- Composition
- Soluble colourant dissolved in solvent
- Common in
- Fountain-pen and some ballpoint inks
- Analysis method
- Thin-layer chromatography (TLC)
Common questions
How does thin-layer chromatography reveal information about a dye-based ink?+
Because the dye is fully dissolved rather than suspended as particles, TLC can separate the mixture into distinct resolvable spots based on how each dye component migrates through the plate, producing a chromatographic pattern that can be compared against reference inks.
Why does the distinction between dye-based and pigment-based ink matter in document examination?+
Dye-based inks are generally soluble and separate cleanly on TLC, while pigment-based inks contain insoluble particles that behave differently under the same solvent system, so examiners must know which type they are dealing with to choose an appropriate comparison method.
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...
- 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...
- Pigment Ink
- Insoluble colourant (carbon black, titanium dioxide, organic pigments) suspended in a binder. Pigment particles do not migrate on TLC, so Raman, FTIR...
- 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...