A matter of choices because, most of the time, the "keep" and the "kill" are so inextricably associated than you can't remove one without loosing the other. Rust and Patina. Remove the rust and you kill the patina. Keep the patina and the rust will slowly digest your beloved collector. Some people refuse to touch to the patina, or even to clean the object: the dust is part of history.
On my side, I have no ready made philosophy or religion on the topic. I just decide case after case, depending on the condition of the nose flute, its rarity, what I'm sure (or not) to achieve decently, etc.
I got a totally wrecked Humanatone and decided to restore it, with my simple means. The nose flute was deeply rusted, and the box, according to the seller, « was run over by a horse, stuck to a bicycle tire and ended up on the front of a train! (Kidding, of course) It's a mess! ». Hahaha! No humour there, simply the truth! :)
1.- The Nose Flute
This is a very common vintage Humanatone, so the loss would not be enormous in case of failure. On the other hand, the rust on the airway cover is impressive, thick and hard, softly killing the Hum, like a daily dose of lead in the kidneys. There is also rust at the base of the flaps, here and there, and also a lot inside the air intake... Yes, there is also a smooth mate grey patina... that will vanish when the rust is removed. Hamletian choices, to clean or not to clean...
First I used a soft metal brush then very fine steel wool (0000), both in conjunction with WD40. I very gently rubbed the nose flute, particularly the air cover, during about one full hour, regularly using a new piece of steel wool and adding drops of WD40. I got a first promising result: most of the rust was removed (patina too...). The air cover surface appeared to be rather deeply gnawed and ulcerous.
It was the time for a bath... I put the Humanatone in a warm Rustyco solution during an hour (I'm not a share holder, but this product is very helpful. It turns rust into black and stabilized oxide).
Then I rubbed again the instrument with 0000 steel wool, rinced and dried the flute, and finally coated it with a not stinky mineral oil.
The result, far from being perfect, is acceptable on the balance between cleaning/preservation and respect of the 'vintageness'. Even the interior has been de-rusted (I also used many Q-tips to rub into there).
2.- The Box
The box is a real wreckage. It is torn, crumbled, and many little parts are bristling on the angles...
But the box is complete! No big part missing, and better — if I can say it – it has been torn all along a side, allowing to spread it flat. That's what I did, and began to soften the cardboard by steaming it over a boiling pot of water. The thick cardboard must not get soaked. So the process took several minutes on both sides, with a gentle steam flow, to reach and soften the inside of the cardboard.
Then and immediately, I ironed the box between flat carboard and a sheet of paper (iron set at max). Then I returned the cardboard and applied the iron the same way. I did the process twice (steam and iron again).
Finally, I placed the box under a pile of books during the cooling and drying time.
Then came the time of the reshaping. I began with a careful gluing of the little splinters back to where they belong, using the minimum instant glue possible.
After all the splinters were in place, I folded the box back to a parallelepiped, and glued the edge along where it was torn. The result certainly doesn't look mint, but the box is complete and has gotten some stiffness back.