A method and ink composition are disclosed that utilize two mechanisms for the purpose of indicating the approximate age of an ink that has been deposited on a writing surface.
The first mechanism relates to detecting color shifts of p H sensitive compounds in the ink as the result of the evaporation of certain acidic or basic chemicals thereof.
The spectral characteristics of the ink are determined in units of percent reflectance of the active compounds in the ink so that the age of the ink can be computed by reference to known reaction rates. In this regard, time dating an ink is dependent upon the composition of the ink and may be determined through analysis such as solvent extraction and spectroscopy.
A plurality of dyes having differing reaction rates may be added to the ink to enable precise measurements to be made over different time intervals. Field of the Invention The present invention relates to an ink and to a method for measuring the age of the ink that has been deposited on a writing surface, and is particularly adapted for analyzing signatures and writings to determine the age of the signature or writing and the age of the signature or writing relative to other signatures or writings. The age of ink deposited on a document may be detected by spectroscopy, as suggested by V. However, time dating analysis based upon conventional ink compositions has been found to yield inaccurate results, whereby such results are not accepted with a large degree of confidence.
2 is a dual line graphical illustration of the peak ratio of yellow light (420 nm) to red light (570 nm) plotted as a function of time in days; FIG. 4 is a dual line graphical illustration of the reflectance spectrum of yellow light (420 m) and the reflectance spectrum of red light (570 nm), including a first plot for an ink which has just been deposited and a second plot for an ink which was deposited at a different time; FIG.
5 is a specifically scaled graphical illustration of the peak ratio of yellow light (420 nm) to red light (570 nm) plotted as a function of time in days which corresponds to the plot of FIG. 6 is a graphical illustration that is similar to the illustration shown in FIG.
If compound A in the ink is transformed to compound B at a known rate once the ink has been deposited on a writing surface and exposed to the air, a simple quantification of the ratio of A to B can be measured using standard non-destructive analytical techniques, including spectrometry.
The elapsed time is then determined from predetermined calibrated time curves.
p H shifts will change the composition of the ink by promoting a chemical reaction.
Further, the use of a ratio facilitates spectroscopy, a well known non-destructive method of measuring the components present.
Performing a time dating analysis of an ink having time dependent characteristics includes the steps of first measuring the spectral characteristics of the ink in units of percent reflectance and then referring to known reaction rates.
The present invention is particularly applicable to investigations that are intended to combat fraud, including medical fraud, insurance fraud, and fraud involving other time dated documents such as wills, trusts, deeds and legal agreements. Background Art The aging of ink is an important factor in the forensic examination of documents. Reed, entitled Forensic Examination of Ink and Paper, which is published by C. In fact, no conventional ink is known having a composition which lends itself to an accurate time dating method.
The ability to accurately time date writings and signatures deposited on a document, or set of documents, can help determine the authenticity of the document or documents and detect fraud, such as, for example, where a document contains several time dated entries which indicate a long span of time, but the writer falsified the document by making the entries all at one time or at a fewer number of sittings than indicated by the dates written on the document. One of the most common techniques of falsifying documents and perpetrating document fraud is the act of entering multiple time dated entries at one sitting, rather than at successive times.