The base material was always stainless, which from some sources I understand cannot be plated. HOWEVER, the fellow who restores the originals for me (I have one set of restored guaranteed to be original arch trim FOR SALE - unashamed plug ;] ) says they were flash chromed over the stainless, but I am skeptical. Why, because I cannot see the difference in unrestored arch trim, there should be some color difference. I am familiar with metallurgy being a retired engineer. It is possible he is telling me that and it causes him to have to spend huge amounts of time sanding the chrome off so he can charge me more. If he wasn't so incredibly good at making junk into something like new I might not be using him, but there it is, MAYBE they were flash chromed stainless steel, but they were always stainless steel, at least every one I have ever seen and it has been more than a few. Purchased a lot of them from Germany, all the same, stainless.
Have I beaten this particular dead horse enough yet? ;]