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Some historical electrical devices used materials that require careful handling. Old switches and scientific equipment can contain mercury, while older electrical components may contain substances that should not be opened or damaged casually. Certain vintage painted surfaces may contain lead compounds. Industrial components can retain oils or chemical residues. None of these possibilities can necessarily be identified from an object’s external appearance, which is why cautious handling is sensible until its nature is understood.
Unexploded ammunition and military ordnance create an even more serious concern. Objects recovered from battlefields, military sites or old storage areas should never be struck, drilled, heated, cut or dismantled simply to discover what is inside. If there is any reasonable possibility that an unidentified object could contain explosive material, the safest response is to leave it undisturbed and contact the appropriate local authorities or qualified professionals. Curiosity is never worth creating an unnecessary physical risk.
Electrical experimentation can be dangerous for similar reasons. Finding wires or terminals does not mean an unidentified vintage device should be connected to a modern power supply. Its original voltage may be unknown, insulation may have deteriorated, and internal components may have failed. Applying electricity can destroy an otherwise collectible object and can potentially cause shock, fire or other hazards. Identification should come before attempts to make an old device operate.
Heating is equally inappropriate as an identification technique. Different metals, residues and sealed materials can react unpredictably to high temperatures. Even cleaning chemicals should be selected carefully because they can react with old finishes or remove historically useful information. The safest first stage of investigation is almost always non-destructive: photographs, measurements, visual inspection and research.