Revolutionary in aluminium, my old trumpet (7)
I believe the answer is:
alchemy
This could be a double definition.
'revolutionary in aluminium' is the first definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'my old trumpet' is the second definition.
I can't judge whether this defines the answer.
Can you help me to learn more?
(Other definitions for alchemy that I've seen before include "Old form of chemistry" , "Medieval activity to turn base metal into gold" , "Chemistry's forerunner" , "Pseudo-science that sought to turn base metals into gold" , "old science" .)