How to Process Thermal Paper for Prints

Thermal paper requires special processing for fingerprints.

Police and criminal investigators need to know how to identify fingerprints on every type of material imaginable. Thermal paper was once widely used in fax machines and is still used in ATMs and credit card machines as well as some printers. Since thermal has a special coating that changes color when heated, a special procedure is required to develop prints on thermal paper. It will take several days to do properly but could be the procedure that delivers important evidence in a case.

Things You'll Need

• Gloves
• 1,500 ml acetone
• 40 grams ninhydrin
• Shallow dish or pan
• Glass stirring rod
• Blotter paper
• Scissors
• Ventilation hood (recommended)
• Plastic bag with seal

Instructions

1. Put on the gloves and turn on the ventilation hood.

2. Pour the acetone into the shallow dish or pan. Add the ninhydrin and stir with the glass rod until it is fully dissolved.

3. Cut two pieces of blotter paper to the same size as the piece of thermal paper you are examining. Dip each piece of blotter paper into the acetone solution so that they are soaked through.

4. Remove the blotter paper and allow it to dry for a few moments under the ventilation hood or in an open area with constant air flow.

5. Sandwich the thermal paper between the two pieces of damp blotter paper. Seal the papers in a plastic bag.

6. Wait at least three and up to seven days. Remove the paper from the bag and remove the blotter paper. Inspect the thermal paper; any prints should now be visible.

Tips & Warnings

• These chemicals should be used only in a location where a ventilation hood is available. If you do not have a ventilation hood, proceed at your own risk and only in a well-ventilated area with continual airflow.

References

• Southern California Association of Fingerprint Officers: Procedure to Develop Latent Prints on Thermal Paper
• Patrick Finch: The Uses and Hazards of Thermal Paper