The copper vessels turn greenish and silver articles turn blackish when kept open in air for long time.

If copper vessels are kept in air for long time, greenish layer of copper carbonate is formed on its surface.
When silver ornaments are exposed to air for long time, they turn blackish due to formation of the layer of silver sulphide.
Hence, The copper vessels turn greenish and silver articles turn blackish when kept open in air for long time.