Re: chrome / nickel plating
Chromium plating is an expensive process. Consequently, the plating layer is often very thin - just a few tenths of a thousanth of an inch.
If done properly, the chrome would have been applied over copper and nickel base coats. As already mentioned, the chrome has likely worn through over a period of time to expose the nickel. This being the case, it is likely the manufacturer skimped on the chrome thickness. To be fair, they probably didn't anticipate their product being around for so long.
To my eye, nickel plating - when polished - is a much nicer finish. However, it is incorrect for most post 1930 bikes. If my memory is correct, Triumph were one of the first to introduce chrome in 1927.
The introduction of chrome didn't happen overnight though; it took several years to gain universal acceptance. Some products were offered with chrome as an option during the introductory period (Rolls-Royce motor cars were offered with a choice) and many after-market products - lights for instance - were still only available in a nickel finish well ito the late thirties.
If your mid-twenties classic has chrome and you want to be correct, it will strip back to nickel in seconds, but you have to go to the platers.
Nickel needs a lot more elbow grease, but it is displays a beautiful pale-yellow patina. It is also less shiny when compared to chrome, so surface imperfections do not show as badly.
David Fryer, Queensland, Australia