Aging Index (Aginsky)
Definition
The ratio of phenoxyethanol concentration in an unheated (cold) extract to its concentration in a heated extract from the same ink stroke; decreases from near 1 in fresh ink to near 0 in aged ink, providing an estimate of relative or absolute ink age.
- Measures
- Ratio of cold-extract to heated-extract phenoxyethanol
- Fresh ink value
- Near 1
- Aged ink value
- Near 0
- Application
- Estimating relative or absolute age of an ink stroke
Common questions
Why compare a heated extract against an unheated one instead of measuring phenoxyethanol directly?+
The heated extract represents the total phenoxyethanol still present in the dried ink, while the unheated extract reflects only what is readily evaporable, so their ratio isolates how much of the original solvent has already evaporated with age rather than requiring an absolute baseline concentration.
Does the aging index work equally well on any age of document?+
No, it is most informative on relatively recent ink because the ratio approaches its floor near zero once most phenoxyethanol has evaporated, after which further aging produces little measurable change and the method loses discriminating power.
Related terms
- ASTM E2494
- ASTM International's Standard Guide for Using Ink Examination Methods in Questioned Document Investigations; sets out the recommended tiered analytical approach, uncertainty reporting...
- Dye-Decay Dating (LaPorte Method)
- An ink dating method that uses HPLC-PDA to monitor the relative concentrations of specific dye components and their degradation products; the ratio...
- Machine Direction (MD)
- The direction parallel to paper travel through the papermaking machine; cellulose fibres preferentially align in this direction, making machine-made paper stronger and...
- Optical Brightening Agent (OBA)
- A fluorescent compound added to paper pulp or coatings that absorbs UV-A radiation and re-emits it as visible blue light, making paper...
- Plateau Effect
- The upper age limit of ink solvent-loss methods (approximately 5-7 years in most storage conditions), beyond which phenoxyethanol has been substantially lost...
- Rag Paper
- Paper made from cotton or linen rags, yielding long, low-lignin cellulose fibres; the dominant writing-paper substrate before approximately 1870 and still used...
- Solvent-Loss Method
- An ink dating approach that measures the residual concentration of semi-volatile solvents (particularly phenoxyethanol in ballpoint inks) relative to a non-volatile reference;...
- Terminus Post Quem
- Latin for 'limit after which'; in document dating, the earliest possible date for a document, established when a material component (paper, ink,...
- Watermark
- A pattern formed in paper during manufacture by localised fibre-density variation on the Fourdrinier wire; visible in transmitted light as a lighter...