Use of atomic force microscopy in the forensic application of chronological order of toners and stamping inks in questioned documents

• The crossing sequences of toner and stamping ink were investigated with AFM method.
• Physically removing the toner and checking the material below it.
• The result of the blind test was different from accuracy between experienced groups and inexperienced ones.
• AFM method is useful when the crossing area is very small.

This paper describes the application of the atomic force microscopy (AFM) as a nano-indentation method and introduces a new method of identifying the chronological order of the application of the toner and stamping ink on the surface of documents by removing either of them. Various toners were used as samples for the AFM nano-indentation method. The chronological order of the application of the toner and stamping ink with either the toner placed over the stamping ink or the stamping ink placed over the toner, could be identified, regardless of the kinds of toners made by various companies. This paper provides the new approach for physically removing the toner and checking the material below it to identify questioned documents, which allows the method to be used to appraise documents forensically. Blind testing has shown that the method to analyze the chronological order of toner-printed documents and the seal stamping on them could accurately identify the order in all samples, while minimizing damage to the samples.