Identifying copper alloy
Copper, bronze, and brass — telling them apart.
Copper alloys cover pure copper, bronze (copper + tin), brass (copper + zinc), and gunmetal. By eye they are hard to separate, which is why cataloguers write “copper alloy”.
Fresh copper is salmon-pink; brass is yellow; bronze is warm brown. But corrosion masks all of this — judge only from a clean break or scratch, never the surface. Some objects were also tinned in antiquity, and a silvery skin on a copper-alloy find is more often tinning than silver.
Green and blue corrosion products (verdigris, malachite, azurite) are typical of buried copper alloys. Stable green that follows the form is good; bright powdery pale-green spots can be active “bronze disease” and need attention.
If you suspect bronze disease, keep the object as dry as possible, store it apart from other metal finds, and ask a conservator before touching it further. Record the corrosion colours and where they sit — they are part of the evidence.