Infrared inspection of WW2 camouflage German helmets

The German steel helmet is an icon of the last world war and it is highly appreciated by militaria collectors. From the period between the first and the second World War to August 1943, decals referring to the service branch were applied to the German helmets. In order to minimize their visibility the soldiers often covered the helmets with a camouflage paint, sometimes mixed to sawdust and sand. Infrared pulsed thermography was used on different kinds of camouflage German steel helmets of the Second World War, to detect the presence of decals. In most of the cases only the shape of the decal clearly appeared in the IR images. In some cases the paint surprisingly resulted to be transparent in the infrared radiation waveband from 3 to 5 μm used by the IR camera, thus allowing to see the drawing inside the decal. Navy helmets were produced in fewer numbers and they are therefore more desirable for collectors. Navy and Army decals had the same external shape and the same internal drawing of an eagle on a swastika. They only differed for the color and the thickness of the eagle and the swastika due to a particular multilayer production process used for Navy decals. This work also describes a procedure capable of distinguishing Navy from Army decals, even when covered by the camo paint.