Pulse thermography identification of service insignia in Second World War camouflage German helmets

The present study aims at detecting and identifying the service insignia possibly present under the camouflage paint of Second World War German helmets, using infrared pulse thermography, a nondestructive IR technique based on the application of a short heat pulse, obtained by a flash lamp. While in most cases, IR thermography allowed to detect the insignia under the paint, in other cases sand, sawdust or woodchip added to the camouflage paint, in order to give it a rough and less reflecting texture, showed to be capable of preventing their detection. In 28.57% of the cases, the one or more layers of camouflage paint showed to be semi-transparent in the infrared waveband 3-5 μm, thus allowing to see not only the decal shape, but also the drawing inside the decal contour.