As hunnymonster says, they may or may not be bakelite.
Bakelite was formulated with phenol and formaldehyde, both have distinctive smells, but the formaldehyde smell is quite unpleasant (and dangerous - the formaldehyde vapour coming out of insulation panels, etc, in old buildings is what gave rise to 'sick building syndrome'). Bakelite is thermosetting - it is plastic during creation but hard and rigid once set - it will not become plastic again when heated. It becomes discoloured (black bakelite goes a lighter brown colour) and loses its shine over time. If it is held under hot water for 10 secs or so, dried and sniffed it should smell like old medicine cabinets - you can get the same result by rubbing it briskly with a finger then sniffing the finger - usually.
Rubber, unlikely as it may seem, was a popular scale material. Materials formed from rubber include ebonite and vulcanite, sometimes called 'hard' rubbers. They were formed with the use of sulphur, so can emit sulphur gases and even sulphuric acid (little beads of moisture on the surface are sulphuric acid, once the material begins to break down). Ebonite (trademarked by Goodyear) was used for things like pipe mouthpieces, bowling balls, ink pens, musical instrument mouthpieces and electric plugs. It had 30 - 40 per cent sulphur content. Vulcanite was trademarked in england by Hancock and the early stuff used mercury to cure it. Vulcanite/ebonite are more or less the same thing, but ebonite rod has the reputation of being purer than vulcanite. Vulcanite goes a greenish hue with oxidation. The green colour can be removed by bleach or boiling water. The surface will have to be buffed again, though.
UF (urea formaldehyde) is another thermo-setting plastic, it is simply identified by the fishy smell it gives off when burned. It can also give off a smell of formaldehyde when it degenerates.
Then there is parkesine, xylonite, catalin.....
Regards,
Neil
