Photo: Original unapplied decals are best protected by clear acid-free containers.
Helmet decals printed "face down" were applied using lacquer as the transfer medium. A thin coat of lacquer was applied on the backside of a decal and it was then pressed against the side of the helmet so that it would bond with the paint surface. Decals were allowed to dry for about one hour after which the protective transfer paper was removed. The decal was then typically coated with another layer of lacquer that was either hand brushed or spray painted over the surface. This protective layer of lacquer was not always applied.
Many surviving examples show that even without the additional protective coating these decals were very durable and resistant to wear. Unlike original decals, modern reproductions are applied using techniques which do not replicate the original application procedure. As a result, most reproduction decals scrape off the surface of a helmet quite easily even if coated with a protective layer of lacquer. Some collectors submit observations that indicate some decals were applied using a "brownish glue" for adhesion to the helmet surface. However this application technique was not readily utilized for durability reasons. It is likely that the "brownish glue" that is being seen along the edges of the decal is actually the transfer medium used on the backside of the wartime manufactured water-transfer decals.
A wide variety of decal designs can be found on World War II German helmets. This includes not only combat helmets, but also political and civil organizations as well. The Germany Military utilized several different helmet decals to distinguish branch of service. The German Army (Heer), Navy (Kriegsmarine), Air Force (Luftwaffe), and Armed-SS (Waffen-SS) all utilized helmet decals to distinguish the men of their organizations. Police units, both civilian and military also used decals as did those who served with fire fighting (Feuerwehr) brigades.
However, as the war progressed factory application of helmet decals was eventually eliminated. By the later years of the war few combat helmets had decals applied. The only military formations that continued to use double decal helmets were combat police units and men associated with the very small number of foreign volunteer (Freiwillige) units serving with the Army, Luftwaffe, and Waffen-SS. This accounts for the many reasons why period photos show troops with a variety of helmets with some having decals and others without.
Original National Shields on Transfer Paper.