Gold on a zinc and silver backing material (7)
I believe the answer is:
organza
'material' is the definition.
(organza is a kind of material)
'gold on a zinc and silver backing' is the wordplay.
'gold on' becomes 'or' (I can't explain this - if you can you should give a lot more credence to this answer).
'zinc' becomes 'Zn' (Zn is the chemical symbol for zinc).
'and' says to put letters next to each other.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'backing' is a reversal indicator.
'a'+'zn'+'ag'='aznag'
'aznag' written backwards gives 'ganza'.
'or'+'ganza'='ORGANZA'
Can you help me to learn more?
(Other definitions for organza that I've seen before include "Thin stiff natural or synthetic fabric" , "Stuff" , "Transparent silk material" , "Silky cloth" , "Thin material" .)