To solve fraud cases, a new technique can determine whether a fingerprint appeared on a piece of paper before or after text was printed.
An example in which this technique would be useful is a situation where someone is accused of tampering with a will or contract by printing on top of it. Determining when a fingerprint was made on the document could strengthen any other evidence.
Experts at Foster and Freeman have created a technique which can achieve this. Pressing a layer of gelatin to lift the print can result differently whether the fingerprint was on the paper before or after printing.
The process involves peeling off the gelatin and placing it inside a vacuum sealed glass boxed which is filled with a vapour of disulphur dinitride. The disulphur dinitride will then bind to the microscopic fingerprint ridges printed on the gelatin surface resulting in a blue coloured fingerprint.
The team tested a print that had text over it and compared it to another that was made on top of the printed text. They found that the gelatin touches the text inside of the fingerprint first meaning that the pattern developed at the end of processing was noticeably different. They then could tell which came first.
So far, they have only tested on fingerprints and laser jet inks, although they have plans to expand the method to other types of printing e.g. writing with ballpoint pens, relevant for signature fraud.
