Recent studies have revealed the possibility of using a fungal strain of Beauveria bassiana on copper-alloy artefacts to convert chloride-induced corrosion products into more stable copper oxalates. This study aims to determine the modifications resulting from the green treatment of active corrosion, focusing on archaeological copper surfaces with pitting corrosion and/or tinning. Results showed that synthesised copper chlorides were transformed first into copper hydroxychlorides and then copper oxalates. A development of copper oxalates was also observed on artificially corroded coupons. Moreover, the treatment demonstrated the stabilisation of the active corrosion present on archaeological objects. On tinned surfaces, copper oxalates formed mainly where the tin layer was lacking.