Tarf derailleur

What a magnificent device this is!

Piero Taruffi, in addition to being the manufacturer of this derailleur, was also a world class motorcycle and racing car driver, designer and engineer. Here this is reflected in the unusual use of highly formed sheet steel and in the way that the organic 'aerodynamic' aesthetic owes nothing to anything else on the market at the time.

Details that I like include:

The highly offset pulley cage - giving a reasonably constant chain gap and, quite probably, a crisp gear change (at least for the time).
The toggle chain has a very long threaded end and a crossbar built into the chain. This allows you to adjust the free length of toggle chain to give a low gear stop - preventing the cage from going into the spokes of the wheel.
The Art Deco 'Tarf' logo.

Details that I don't quite understand include:

The system of springs. The large silver outer spring seems to be largely concerned with the sideways movement of the whole pulley cage (although it also contributes a small amount to chain tension). The black inner spring is a complex double-wound item that seems overkill for the simple job of tensioning the chain - but that is all it seems to do. A little tweaking and it seems to me that the silver spring could have done both jobs.
The finish on the outer pulley cage plate. This seems to have been deliberately roughened and, perhaps, finished with some black 'crackle' effect.

Finally I should note that, for a derailleur that appears to have had relatively little use, the plating seems to be in surprisingly poor condition. Something that would be familiar to owners of mid-20th-Century Italian motorcycles.