Preliminary Studies on the Absorbance Ratio Method Used to Determining the Age of Stamp-pad Ink Seal.

Stamp-pad ink seals are often placed on important documents, and determining the dating of stamp-pad ink seal is important to assess the authenticity of a document. In this study, 20 different brands and types of stamp-pad inks were classified by ultraviolet visible spectrophotometer. Six different brands and types of papers were classified by micro-Fourier transform infrared spectrometer and visual spectral comparator 6000. Three different brands of stamp-pad inks and two different types of paper were used to make diachronic samples of the seals. A method was employed to date the stamp-pad seals by comparing absorbance ratios and inks of known age. Curves were created to show the relationship between the absorbance ratio of ink and the age of the seals. The experimental results showed that the absorbance ratio method was applicable for the relative dating of stamp-pad ink seals in some cases where the seal was placed on the document within 10 weeks.