Change put behind a mirror (6)
I believe the answer is:
silver
'change' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for silver that I've seen before include "Long John - -" , "Grey-haired" , "Change - Ag" , "old folk?" , "Silver of precious metal" .)