Brunelle R-Ratio Method
Definition
Dye-degradation method (Richard Brunelle and Kenneth Pro, 1972, later refined). Tracks the ratio of extracted and unextracted dye over time to estimate ink age.
- Authors
- Richard Brunelle, Kenneth Pro
- Year
- 1972
- Measures
- Extracted vs unextracted dye ratio
- Purpose
- Estimate relative ink age
- Field
- Questioned document examination
Common questions
What does the R-ratio actually measure?+
It compares how much of a dye component can be solvent-extracted from the ink line to how much cannot, a ratio that shifts predictably as ink components degrade or bind to paper fibres over time.
What limits the reliability of the Brunelle R-ratio method?+
Results depend heavily on storage conditions such as heat, light and humidity, so the method estimates relative age between comparable samples rather than giving an absolute calendar date.
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...
- 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...
- 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...