Thanks, I just thought maybe there was a standard finish that Yamaha used then.
Most likely they did.
However, I can recall a long time back I stripped one of the early benches that came from Yamaha in the late 50â€™s early 60â€™s.
It was one of those pianos finished in what Yamaha called limed oak; this yellow pecan colour over a very strange grade and grain of wood.
The outside coats stripped off like no finish I had ever seen before or since. The dichloromethane stripper would not penetrate in the usual way and the finish came off more like an early plastic than any type of lacquer or other type of wood finish.
I would test the finish first to see what you have previous to applying anything to remedy. Try an area that does not show like along the cheek below the cheek blocks.
Yes do not use anything without knowing what is the finish. Petrol based products can make a mess with some finishes, penetrate and soften it.
If a streak have a white bottom it is polyester (chances are that it is).
Black polyester on Yamahas : the hard and shiny coat is very thin. Under it there is a more grey and more supple bottom coat that you cannot polish (so sanding and polishing black polyester on those pianos must proceed with caution)
If the shiny coat have been sanded too much you have grayish surfaces, and the finish cannot be polished.
If the case is in wood, this is yet possible a similar finish have been used. In that case I suggest that you may use French polish (after surface prep) or even a simple wax (or automotive wax) those will need to be stripped to refinish the piano anyway.
French polish (the fast variety - contain some shellac waxes and fast solvents possibly - which is easy to rub - ask Douglas Gregg about where to find it) can bring back a nice gloss, and the job can be done by a dedicated amateur, with a good arm and some "arm's oil".
The prep can be a fine water sanding for transparent gloss, or even a rubbing with fine scotch brite on a leveled surface, for a black shine.
Dan, for waht I know, polyester is stripped with heat guns. paint strippers does not relaly work, unless very large quantities are used, covered, by a plastic film left a few hours, strip, and go again... hard work.
The undercoat on Yamahas is may be not Polyester but possibly PU (lesser cost) but I also have been said that a bottom coat is used to be in Polyester, then a high gloss coat is sprayed that can be polyester (special high gloss for pianos) or Polyurethane.
The undercoat is supposed to be a little supple so the top coat does not crack. But 1961 finishes where not as good as of today and old polyester are often crocodile looking !)
A common solution used was also the spraying of "shellac" (in fact a mix of cellulose and shellac in Nitro solvents) with final coats sprayed or hand rub, and a last high gloss obtained by rubbing benzoil (Benjoin) - case of some German instruments from that era and up to 80's certainly.
The bottom coat whiten and crack with time, often.
The surface can be sanded and rubbed with shellac with good results , only if the bottom is clean.
"amalgamator" , may be, but not many polishers trust in that product, mostly used to finish/rub the gloss of mixed products cellulose/shellac/wax (name is "mattine" in French)