Amalgam is identified straightforwardly, in modern chemistry, as an alloy of mercury with another metal, a well understood category of material with no real ambiguity in the general chemical concept, though the specific composition, which metal, in what proportion, varied considerably across historical recipes depending on the intended use, whether fire gilding, ore refining, or another application entirely.
The historical importance of amalgam lies less in any identification puzzle than in its documented human cost: both fire gilding and amalgamation based ore refining exposed enormous numbers of pre-modern and early modern workers to serious mercury vapor and mercury compound exposure, and historians of technology and medicine increasingly treat the mercury amalgam trades as a significant, if historically underrecognized, source of occupational poisoning across several centuries and several continents, a sober counterpoint to the genuine technical cleverness of the amalgamation process itself. Modern dental amalgam, still in limited clinical use today, is formulated and handled under safety standards the historical gilding and mining trades never had access to, though the practice remains debated precisely because it continues the same basic chemistry that caused so much harm in its earlier applications.