Itxaso San Román, Luis Bartolomé and Rosa María Alonso allowed the chemical compound to age under normal conditions, without ageing it artificially, which is what happens in other methods, and studied its evaporation speed.When analysing the kinetics involved in its disappearance, the research group established a pattern that links the state of the ink with the time that has elapsed.These two ink aging methods are the Sequential Extraction Technique (SET) and Solvent Loss Ratio Method (SLRM).
To do this, they used BIC® ballpoint pens, one of the most common makes and, therefore, the most widely used in documents subjected to legal examination.
Each document was produced at different moments using a different ink stroke pressure, factors that may alter the results and lead to dating errors.
During the natural ageing process of each sample, which had a known age, the research team analysed the evolution in the various volatile components.
Specifically, they focussed on the solvent known as 2-phenoxyethanol (PE), present in 80% of the inks in ballpoint pens of this type.
There are four major approaches (each approach is a group of methods) used for dating inks on documents: 1.