Well I couldn't wait to get started on the cleanup of this lid so I made the job over the last weekend.
As the liner was already detached from the non-existant band there was no harm in giving it the final bath of its life. It's been through damp and dry through all of its years in the ground so i figured one last final soaking couldn't do any more harm. As it dried I added several applications of leather care paste, I know the purists will say this stuff doesn't help dead leather and may hasten its eventual demise but as this liner was (a) heavily soiled (b) heavily damaged and (c) dried out like a potato crisp I figured it couldn't get any worse. As the paste did soften the liner somewhat I took the opportunity to 'form' the liner into a more original shape with some paper clips around the tears and support from some AA batteries which happened to be the right height. Now the liner is dried quite hard again but at least its clean, a better color, in a better shape and also smells pretty!
Amazingly all the leather tangs were intact but they were all bent out of shape so again while the leather was damp and soft from the paste I used the paste bottle to flatten them out so they're now dried again in an even pattern.
I plan to somehow refit the liner for display purposes but with the outer and inner bands nothing more than crumbled rust I have yet to come up with a cunning plan in this regard.
The shell got a soap and water bath with regular scrubbing with a green scouring pad and judicious use of a plastic knife which soon wore down to a nice chisel shape as the sandy Italian soil had solidified to something akin to concrete and was hell to shift. After about 2 hours of this I then went down the Oxalic acid route.
I let the lid soak for 15 minutes in a 100g acid to 8L water solution then proceeded to spend another 2 hours scrubbing and scraping then soaking again in 5-10 minute intervals. Slowly the encrusted soil could be removed and the result I think is quite an improvement over the helmet as shipped to me. Even the decal remnants came up to such a degree that the decal is recognizable.
The right side of the helmet was impossible to clean up, that concrete-like substance just would not move! Something with the way the helmet was buried must have added to this encrustation as the worst of the interior rust was also on the inner right side of the helmet and the wire had also rusted away on this side. Maybe the helmet was buried right side down where the majority of the ground moisture accumulated?
The lower arm of the swastika I found to be reasonably intact, perhaps protected from wear by the wire above it? Anyway, a neat find I think.
Rear shot, definately an improvement over how I received the lid and after a coat of Reanaissance wax to seal everything up, this M40 is ready to join my M35s in the relic collection.
sweet, turned out really nice.