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Since they are new...since the 60's there are probably no problems at all. Then plastic polish would work well.
~Richard
Older Black scales are often Hard Rubber or Bakelite.
Toothpaste and then...

Good question!
If the plastic in transparent colors or crackle looking cover over a white inside, the scales may be in doubtful condition.

Some molded plastics also can be iffy. The ones...