Unpainted

Near-synonym: paintless

Perhaps the surface of the red brick, long unpainted, had scaled off a little more here and there.

The new cars incorporate many features first introduced in the 1938 tube stock, but major changes include the use of rubber for the bogie bolster and axlebox suspension, fluorescent lighting, and the panelling of the cars in unpainted aluminium alloy.

A few unreliable-looking boats were beached there, unpainted boats built largely of gray driftwood, or so it seemed to me.