After many years of restoring stahlhelm in all forms of livery, just thought a few tips I've picked up over the decades may help new restorers out.
Original WW2 German Zimmerit paint is no longer available-there's a surprise!! So, you have a choice. Model paint, modern household paint or automotive paint. If nothing else is to hand, go ahead. With practice, almost any paint can be made to look as it should. I am not going to give away any ageing or distressing tips-these are trade secrets BUT, buy a cheap helmet as a "control" for the paint before putting it on your prized posession.
In the 1950-75 period, most household paint contained high degrees of lead. What you now buy in B+Q is nowhere near as good for helmets as the early stuff. Oil based is the best-most are now water based. If you look hard enough-car boots, antique fairs, old established decoraters and suppliers, it IS possible to get early paint. If you're reading this, you already know what an old tin of paint looks like!!
I recently bought some 1960's "Jellipex" gloss in all the right colours from a car boot. Unopened, £2 a tin. It's excellent. Leave it in a very warm place after application, and it will crack and shrink slightly-ideal for aged camo. In the North of England in the 1960's were a small chain of paint stores called Blaskeys. Their own brand gloss is the Holy Grail. Their "Arabian Sun" ( I've got two tins) must be old stock from the Afrika Korps-just right for DAK and Med. camo colours.
I said I would not give away ageing techniques BUT if you are at a car boot and see any 1970's rust preventatives/killers, BUY THEM!! Their contents would give any environmentalist a nosebleed but, used carefully, they will age metal like nothing else-more acid than a 90's rave!!
Lastly, if you do come across any of the above, PLEASE follow Health and Safety basics. It was changed for a reason!!